Tbh (stand back, QS/ATJ fangirl coming through) I think we'll see him again, and we'll see him in a hero costume at some point. I'm thinking Infinity War, but CW is still a possibility. 1) They didn't share the alternate ending. Why wouldn't they if they knew how much people wanted it? Because they still plan on using QS costume and didn't want to waste the reveal on a deleted scene on the dvd. 2) Kevin Feige has said too many times, and enforced it too hard, that QS is dead for good. Marvel exec doth protest too much. 3) ATJ cannot confirm nor deny how many Marvel contracts he's signed for, and when he told the interviewer re: Pietro returning, he was like "Yeah... That's real question isn't it... -cough-" and was smiling, avoiding looking at the interviewer, etc. Classic signs of someone trying to avoid spilling the truth/giving away a secret. If he was out for good, he would say "Yep QS dead, sorry guys." (but even then: Coulson). And then of course, 4) The Cradle. Why hype up the regenerative properties of the Cradle and make it a focal point of the film, only to conveniently forget about it in their time of need: a fallen Avenger, who happens to have regenerative elements to his enhanced abilities that would only help the Cradle do its job.
Boom. Drop the mic. (can you tell I've gone over this a thousand times?
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