Thought about it some. Here's what I would have done, if I were in charge:
Season 5:
Immediately would take place after Rita's death. However, because of Dexter's emotional state, Harry would fade away and Brian would come back and take his place. However, the villains of the season would remain the same, with the Barrel Girl Gang being the primary antatgonists. In order to avoid taking responsibility for his own failures and try to make sense of the world again, he begins hunting down the Barrel Girl Gang (I have always hated that name).
I wouldn't remove Lumen from the picture, but I'd definitely change the relationship between them, with Dexter taking a more protective, paternal stance towards her, subconsciously compensating for his failure to protect and avenge Rita. I'd also build the conflict between Dexter and Jordan Chase throughout the season with them meeting several times, and each time they try to get in one another's heads. I'm thinking Hannibal/Will-esque conversations, but with Chase being only partially successful at digging below the surface. He'd have a real cult leader-like mentality and we'd dig into the cultish nature of the Barrel Girl Gang as well. I always wanted to find out more about Chase and felt that the writing for that character was below average despite a great performance by Miller.
The goal of this season would be to have Dexter's emotional guts ripped open and laid for the audience to see, that he is not just a standard psychopath, but a warped man with real emotion and drive. As silly as it is, the point of this season would be to show 'The Dark Avenger' that sometimes Dexter thinks of himself as emerging. Through the death of Rita, him saving Lumen and stopping the Barrel Girl Gang, and ultimately rejecting Brian, he'd finish the season at a better emotional place than he started at.
At the same time, I would have Quinn investigate Dexter because he genuinely believes that Dexter may have had a hand in Rita's death. Not because of the clinical phone call, but because of Trinity somehow escaping Miami Metro's dragnet and Trinity being present at Metro Miami and coming across Dexter in the previous season.
(putting this scene back into play)
We'd have less stoner Quinn and more dogged investigator Quinn. He'd contact Stan Liddy to assist, but Stan Liddy goes off-back and tries to blackmail Dexter (rather than arrest him so he can be famous again or whatever the fuck he wanted). Dexter doesn't play into the blackmail and instead Lumen kills him in defense and Dexter covers it up as an accidental death. Quinn continues to pursue the case, but Dexter subtly frames him on a drug charge (just to get him to back off). Quinn's superiors demote him to beat cop or something and Quinn backs off for now (as he can't prove that Dexter is responsible). In this way, I want Dexter to evolve a bit. Doakes was gonna be framed as the Bay Harbour Butcher but Lila killed him. I wanted Dexter to find another way to deal with this problem rather than escape, as Dexter discovers that he likes his life.
I'd have Astor, Cody, and Harrison stay with Dexter a little while, but then Paul's parents come back and offer to take them because Dexter is too messed up to care for them. Throughout the series, I'd have him do regular visitations and support them, but they wouldn't live with him (cause they just use those kids as fucking props). One of my favourite scenes is when Dexter beats the shit out of Astor's friend's abusive dad, so I'd retain that scene cause he genuinely is proud of Astor and cares about his kids (as he loves Astor and Cody like his own along with Harrison).
Season ends with Debra arriving late to discover Chase's dead body, tied down with his throat cut open (by Lumen's hand). However, there is a blood slide and other evidence on the scene. While Dexter isn't caught, there's enough physical evidence left behind for Debra and Metro Miami to realize that a vigilante is at work in Miami and begins to pursue this as an active investigation. Lumen leaves and goes home, grateful that Dexter helped her. Final shot is Dexter alone in the Metro Miami HQ. He looks up and sees Rita walk through the doors. It's up to the viewer if it's a memory or a hallucination. He has a slight smile.
Season 6
Season 5 would also use the Doomsday Killer as its antagonist. However, his kills wouldn't be so ridiculously elaborate as we saw. For one, he wouldn't paint these fucking things:
However, his murders would be extremely disturbing and grotesque, nonetheless. The whole Travis/Gellar thing was so obviously telegraphed from the outset, that at the end of the first episode, we'd know that Travis blacks out and becomes Gellar.
Anyway, I'd wanna play it so Dexter stays, I dunno, smart, and doesn't trust Travis at all and begins tracking him. However, Gellar is smart and catches onto Dexter quickly.
Meanwhile, Quinn and Debra take the lead on the Doomsday killings (Quinn's worked his way back into the graces of his superiors by this point). On their own independent investigation, they quickly clue in that Travis is the best suspect and begin hunting him down. Around the same time, Gellar commits a mass murder, leading to a city-wide panic and Metro Miami going draconian on the city in an attempt to find him (think Boston following the Marathon bombing) before his next attack (hell, have Homeland Security in on this shit, it's their job).
However, Dexter has to find him before Homeland and Metro Miami does as Gellar knows his identity (Travis is mostly unaware). Both Dexter and Debra track him down to the church, however Dexter is running late this time. Gellar gets the drop on Debra, injuring her badly. Dexter comes in at the nick of time and stabs or shoots Gellar. Gellar survives and Dexter thinks about killing him. However, the Gellar personality "dies" in the wake of his failure and all that's left is a confused Travis who has become completely deranged but mostly harmless. Dexter takes mercy on him and leaves him to be arrested by Metro Miami (and Quinn who comes in just as Dexter makes his escape). By the end, Travis is in police custody, Debra knows that Dexter is the vigilante, but cannot prove it, and Quinn knows that the vigilante is still active. The idea behind leaving Travis for the police is that Dexter is not only learning and understanding mercy, but that he realizes that some of his extracurricular activities are leading to humiliations and embarrassment of the Miami PD (as they still think Trinity is alive and are wasting police resources on it, resources that could be used for actual cases).
Season 7
This season might play out the same in a lot of ways, but with a lot more Isaak Sirko. Instead of Debra having to deal with that knowledge that Dexter is a killer, she's hailed as a hero despite knowing that it's a lie. She instead begins to investigate Dexter, while keeping Quinn's suspicions at bay. The season becomes a cat-and-mouse game between Debra and Dexter and Isaak and Dexter. At the same time, Dexter gets wrangled up with Hannah McKay (and he does realize and acknowledge that this is a terrible, terrible idea).
I don't have too much objection with Season 7, but I wouldn't have Hannah kill Sal Price, cause frankly... it's stupid. Instead, she'd just play him and leave him looking foolish and humiliated while Dexter destroyed his evidence. However, Sal's zealotry eventually makes it impossible for Hannah to stay in Miami and she leaves. Dexter decides to stay behind as Isaak's hunt is making life dangerous for those closest to him.
Isaak's pursuit of Dexter allows George to try to make a grab for power, and Isaak winds up with a hit on his head. Both Dexter and Isaak are made by the Ukrainian hardcase assassins and they work together to put them down and eventually Isaak is killed, but not before making peace and leaving some words of advice for Dexter, which gets him to realize that he has genuine feelings for Hannah and begin to move on from Rita (cause fuck you Dexter writers, Rita was goddamn important).
However, George is still a loose end ("Isaak asked me to give you a message"), so Dexter goes to finish him off, where he's caught in the act by Debra.
Season 8
No Brain Surgeon. No Psychopath Whisperer. Fuck you, Dexter writers. Here's my Season 8.
Debra grapples with the proof that Dexter is a murderous vigilante (but she doesn't put the pieces together that he is also the Bay Harbour Butcher yet... she assumes that Rita's death has driven him to madness and vigilantism till the second half of the season). She eventually finds out that he is also the Bay Harbour Butcher and that he framed Doakes (but did not kill Doakes).
At the same time, a killer begins to target Miami Metro police officers. Laguerta is the first victim. This killer becomes Dexter's most dangerous adversaries to date cause almost from the outset, he knows that Dexter is a serial killer, which puts Dexter at a disadvantage. Because of all the police and public official deaths, the public begins to panic once again (like during Doomsday). The killer sends coded messages to the police and the press. He also targets public officials like the deputy mayor, the commissioner, city manager, etc.
Doakes returns to haunt Dexter's dreams, a sign that Dexter's conscience is beginning to surface, and eventually these dreams bleed into Dexter's reality as Dexter pursues "The Lawman" (a moniker the press gives to the killer). Doakes' presence helps Dexter work through the case, helps him process it and investigate as he comes closer to finding The Lawman.
(The Lawman is inspired by the Zodiac Killer)
Debra wants to take Dexter in, to get him help, but eventually realizes she needs his help to capture the Lawman.
Quinn is shot and nearly dies at the Lawman's hands, but Dexter manages to rescue him. This is finally proof that Dexter is the vigilante, but Quinn decides to keep it to himself when his superiors interrogate him.
Dexter's kids are visiting him, and they are alone when the Lawman arrives in disguise to give them a message. He doesn't harm them, but it does send Dexter into overdrive into trying to hunt him down. He's baited into a trap and nearly is killed by armed policemen, but manages to escape intact.
Deb, Dex, and Quinn begin to piece everything together, with Deb and Quinn going through official channels while Dex does work off-the-books. However, they are unable to stop The Lawman from bombing Miami Homicide HQ, killing multiple officers and sending the citizens of the city rioting. However, Dexter finally figures out the identity of The Lawman:
Tom fuckin' Matthews! Anyways, turns out he would have been the one who planted the seed for the idea of turning Dexter into a 'directed' serial killer in Harry's head. Cause... he's more like Dexter than Dexter ever could have thought. A similar monster to him, one motivated by boredom and loneliness to see if he could create another thing like him. Of course, by this point, Matthews has gone off the reservation. Dexter eventually corners him, and push comes to shove, Matthews commits suicide. I'd wanna tie this back into the first season, with someone close to Dexter, similar to him, coming out to play, but with a twist on the events.
Series would end in a couple different ways, not sure which way to go:
1) Either Hannah comes back, and Dexter's finally found a measure of peace and stability. He brings his kids back home and settles in for a quieter life, aiding the police when he can, silencing the Dark Passenger when he has to, but he no longer has that need that he did before. He's essentially become 'a real boy'.
2) Before committing suicide, Matthews burns Dexter's identity and disseminates the information publicly. Final season is Dexter on the run with Deb being forced to chase him.
There's lots of other stuff, but these are the broad strokes.
