Few will argue that Patrick Stewart playing Professor Charles Xavier was one of the shining characters in the original X-Men movies. Stewart played the X-Men's leader in all but two of the main X-Men movies, and he also cameoed in both of the Wolverine movies. Following his most recent reprisal of Professor X in X-Men: Days of Future Past, Stewart returning to the series again next year for Wolverine 3. However, after 17 years of playing Professor X, it sounds like the actor will be permanently parting ways with the character.
While speaking with ITV, Patrick Stewart stated that Wolverine 3 will likely be his last performance in the X-Men franchise, though he wasn't willing to say that with 100% certainty. As he put it:
I would imagine this is probably the end of this franchise for me. But the thing about science fiction and fantasy is that you can never, ever say it's the end, it's over.
By the time Wolverine 3 (still officially untitled) is released, Patrick Stewart will have played Professor X across 17 years, which is more than most actors can say for a role. Nevertheless, age-wise, it makes sense that this would be the last appearance of Stewart's Xavier. He was 12 when he met Raven Darkholme in 1944, as seen in X-Men: First Class. Since Wolverine 3 takes place in the future, that means Xavier could be around 100 years old in the story, maybe older. He may be the world's most powerful telepath, but his body is still susceptible to aging, and it's possible Wolverine 3 will see his demise. Still, as Stewart pointed out, this is the realm of science fiction and fantasy. Remember, Xavier died in X-Men: The Last Stand, but later returned in a new body. These mutant powers make the impossible more probable.
Another important thing to keep in mind is that we already have another actor playing Charles Xavier in the movies right now: James McAvoy. Although X-Men: Apocalypse marked the end of the "First Class" trilogy, there's been talk of another X-Men movie that will take place in the 1990s. If that gets greenlit, then there's a better chance McAvoy will be the one in the wheelchair rather than Stewart.
Assuming Wolverine 3 is Patrick Stewart's finale time playing Professor X, he won't be the only actor leaving the X-Men series in that movie. This will also be Hugh Jackman's final time donning the claws of the eponymous mutant. It sounds like the third Wolverine spinoff will be both of their swan songs, and Stewart later added in the interview that he is playing a "very different Charles Xavier" from the ones seen before. If this ends up being his last time in the world of mutants, we can presumably expect him to go out with a bang.
Wolverine 3 slashes its way into theaters on March 3, 2017.