Cap is 50/50 but I think Ironman will definitely die in my opinion. I think he goes all in on stopping Thanos as he feels fully responsible for what has happened. Losing Peter has brought this to the boiling point. He ain’t using no half-measures for this final battle.
Cap is definitely done because his arc is pretty much over. Peggy, Bucky, his relationship with Tony, his role in a modern world, dealing with moral and personal ambiguities. Endgame will wrap up any plot threads and bring his journey to a close. In addition, Cap (and all his ideologies) is much more of a symbol in the universe than Tony, just like Superman. For him to die is more sensible thematically, like a Christ trope. It'd feel weird for him to stick around, especially when the last 2/3 movies he's been in have all centered around him feeling out of place, out of time, and alienated.
Tony still has a lot of plot threads that logically should continue. He has Pepper, Peter, a wedding they were talking about, and seeds have been planted of a kid on the way. Tony has always been meant to survive (the cave escape, stranded in space and somehow finding a way home, paranoia of having survivor's guilt), Cap since his first movie has always been meant to die (sacrificing himself like 50 times, laying down his shield). I could easily see Endgame wrapping up with Tony's big wedding, then Tony retiring and only sporadically appearing in future MCU movies as a "consultant" or super big surprise.
