There was a Kevin Feige interview almost exactly a year ago now (before Infinity War) that's really stuck with me:
https://ew.com/movies/2018/03/09/marvel-studios-kevin-feige-mcu-future/
"
When we talk about resolution or a character’s story ending, are we necessarily talking about death?
People always will jump to that. That’s not necessarily what we’re talking about. I talk a lot, because I’m a big-*** nerd, about Star Trek: The Next Generation, “All Good Things.” That to me is one of the best series finales ever. That wasn’t about death. Picard went and played poker with the crew, something he should have done a long time ago, right?"
Maybe it's just because I'm also a Star Trek nerd
, but that answer seemed and seems important to me. The obvious answer for a character to have an arc like that is Tony will finally, actually settle down with Pepper (which dovetails with that baby answer Gwyneth Paltrow gave). He's blown her off how many times now? I feel like that IW scene in the park before Doctor Strange showed up was there to remind everyone where their relationship was at. You could also send Cap back to the 40s so he could have his date with Peggy (sort of like Amy and Rory being killed off in Doctor Who by sending them to a different time to live full lives), but all the time travel movies ever made make that seem like a bad idea. It would threaten the whole timeline that led up to the MCU.
Cap will die. He threw himself on a grenade before he even had powers. He went down with the plane at the end of his first movie. He has no problem sacrificing himself for others. And honestly? Having him survive won't be as satisfying as having Tony start a family with Pepper. Steve doesn't have any connections in the modern world as strong as Tony-Pepper. I think one of them has to go. This way makes a lot of sense; the other way would be a big gut punch.