Over the past few months, I've heard plenty of discussion on why there could not be an X-Men 4. One of those main reasons being that Xavier is dead. Apparently, after the credits, a bearded man with no consciousness that was used as a lesson earlier in the film by Professor X gains consciousness and says, "Hello, Moira" and she then turns and ask, "Charles?". Apparently the guy is Charles' brother who was born brain dead. Charles takes over his body after his is ripped to shreds.
Once again, I'm not sure if anyone else discovered this on this site, as it has not been mentioned to my knowledge so if this is old news I appologize.
CBM: Here is the clip you're talking about..