Christian Hannah

Chosen answer: As revealed in the post-credits scene, he transferred his consciousness to another body, one without brain function, just before his own was destroyed. He foreshadows this during a lecture early in the film, when he talks about the mind living on even when the body dies. So his mind, his "self", survived, even if his physical form did not. It is widely assumed among X-Men fans that Charles transferred his mind into his comatose twin brother, thereby explaining how Charles later looked and sounded exactly like he did before Jean disintegrated him.