If you had authority to make drastic changes to the show, including killing off cast members, how would you use it?
First, I'd kill off Malcolm. He's done. His story has been told, he's lasted long enough, time to say goodbye. I'd bring Tommy back from the grave to replace him. Like I previously posted, I'd like Tommy to be the one to kill Malcolm. One of the first interactions I'd write between him and Ollie is Tommy informer Oliver that the old Tommy died a long time ago, just like the old Ollie, and insisting Oliver call him Merlyn - just like in the comics, and to differentiate from his father, who most people simply refer to by firstname. It'd also be cool if Tommy made a point of calling Oliver the Green Arrow.
I'd probably next kill off Diggle. It'd be tough, I wouldn't like it, but it's necessary Oliver is pushed into evolving. After Diggle's death, Oliver grows a depression beard that eventually becomes his Green Arrow beard, i.e. awesome. Oliver stops letting his ego dictate his actions, grows up and stops taking himself so seriously, perhaps picking up a sense of humour along the way.
Thea learns that the life of a vigilante isn't it for her, she wanted to learn how to defend herself and not get hurt, but she doesn't want to hurt others, so instead she decides to go college and eventually retakes Queen Consolidated to protect the family legacy and honour Moira. Of course, this would require Willa Holland to become a recurring guest character.
Roy stays with Oliver of course. They become a stronger duo than ever.
Laurel disappears for a while. She eventually returns and comes into her own as Black Canary. She and Oliver get together, thus effectively ending this pairing drama bullshit and the two fight crime together on occasion whilst she does her thing as a lawyer. It would perhaps be cool if Constantine Drakon killed Lance and she goes chasing after him for a while, thus taking her out of the show for a bit.
Felicity can stay part of the crew and do her usual thing.