While details on that are sketchy at best, if Turner is returning, that would seem to indicate a potential role for James McAvoy, not Patrick Stewart. Still, anything is possible.
Of course, the question is, is there a future for Patrick Stewart in the X-Men universe?
For those of us who were there when the X-Men franchise began Patrick Stewart is Professor X. It would be great to see him return.
At this point, there has been no official announcement of a follow-up to X-Men: Apocalypse.