So here's my crazy idea that involves both living past Avengers 4:
What if they let Steve ride off into the sunset with Sharon post Avengers 4, but got Chris Evans to sign on for one more movie a few years after Avengers 4. And that movie was "The Death of Captain America"?
And I'm not talking about Emily VanCamp shooting him with a sniper rifle.
As part of when Amazon put all those digital comics on sale for cheap, I bought and read
"The Death of Captain Marvel", and man it was one of the best comic stories I've read. And it made my kinda sad that they're almost certainly not going to have the Mar-Vell background for Captain Marvel in her movie, so we're probably never going to see that storyline played out in the MCU.
But what if there were someone else in the MCU that they could use to tell a lot of the same story beats, with a lot of analogous charaters? Some of the secondary characters already exist in the MCU (Thanos specifically, but Iron Man and Dr. Strange are there as well, and Spider-Man has a moment in it). And with the MCU as currently set up, you could use currently existing characters to replace the important ones from that story that don't exist yet:
Mentor: Fury
Elysius: Sharon Carter
Eros and Rick Jones: Bucky and Falcon
And you could use the third act to bring villains from both his past movies and Avengers movies as well. And for a real gut punch, have Hayley Atwell play Mistress Death for this part:
I mean, if you want to get really crazy, you could even hint at
the cancerverse version of this story as well.
There's a part or two of the story where there's no real great analogue for now. And even though we have Tony and Strange, I feel like there aren't enough super-geniuses in the MCU right now for the "Why didn't you guys work on this earlier" part of have as much gravity as it does with Reed and Beast as part of the crew. But I feel like this would be the best possible send-off to give Chris Evans as Cap if you're actually going to kill him off and not have him ride off into the sunset as a retiree and stay there.
All that being said, I don't ever see this happening as it's way too depressing of a movie for Marvel to make, but I would be there front and center if they did.