Who Dies, Cap or Tony?
I'm betting Tony. His character arc is pretty much done and I can see him sacrificing himself to save everyone else, like at the end of the first Avengers, only for the last time. He can get a dramatic goodbye scene with Peter Parker who will then have to find another mentor (Reed Richards?)
Killing Cap would just seem mean, after all he's been through, and it wouldn't resonate the same way. I'm guessing after being forced to go underground, he will decide to stay in the shadows, "retire" and pass the Cap mantle on to Bucky or Sam.