“It’s [the] Marvel universe. It was very much our intention to kind of go the way we did. There was a costume designed for whether… if I didn’t [die]. Which was ****ing really cool. I was like, ‘Oh my God.’
I’m not sure if I can really go down that realm, but you know, yeah, it was definitely an alternative, that I think they had to play with. But, it was very much set from the very beginning, and Joss had in mind to tell the story that he told… and I was very game for that, as well, because I think it really gives [the movie] sort of an emotional twist to it. A surprise.”
Aaron Taylor-Johnson Talks Marvel’s Quicksilver Plans [x]
If by “it’s the Marvel universe” he means "no one really stays dead in these films” then we might see Pietro again. But I think at this point he has no clue what they want to do with Quicksilver in these films and quite frankly neither do I.