Re: Changing the roster for Avengers 2?
None of them should or will leave the team. You don't want an X-Men 3 where Nightcrawler is never mentioned and Cyclops is shat on in the opening moments.
The problem with Black Panther or Ms Marvel or Dr Strange showing up is they really do need their respective origin movie(s) first to be done justice. And it doesn't look like Marvel will be working on any of them before Avengers 2.