I don't necessarily agree with VVD's full assessment, but I do believe that Xavier should stay dead.
There are a number of plot devices out there that can be incredibly effective if used infrequently. Killing off characters is one of them, and bringing them back is another. If you kill off an important character, you enhance the story by being able to explore how it effects the other characters in the book and you also leave the impression that anything can happen in the story. Kill off too many characters and it just seems like a cheap ploy.
Then again, bringing back characters can work just as well if used infrequently. It's just, when you bring a character back, you have to look at how your story benefited from the character's death, and what it has to gain from bringing the character back. If the latter outweighs the former, then it's worth exploring. What happened with the 616 Universe is we say way too many resurrections, and very few of them contributed positively to the storytelling. It was a gimmick. Resurrecting characters is effective, but the 616 did it so much that coming back to life wasn't worth ****. It's reached a point that deaths are meaningless now, since the reader knows the character will be coming back, and resurrections are meaningless because it's practically an everyday affair. The UU can benefit from resurrections, as long as they use them sparingly. Beast's resurrection could be a great thing, but I only see Xavier coming back as harming the book.
Beast's death was resonant because of his personal interactions with the characters. Storm was a character who's personality was, in a lot of ways, dependent on Beast. Almost all of her characterization dealt with her relationship with him, and his death sent her life into a tailspin. The results of that are that we've seen Storm develop some (although not as much as I'd like to see) in the following arcs. While Beast's death affected everyone, I think this was really the only major long-term consequences we've seen out of his death. Bringing him back now would be an effective storytelling tool because it allows Kirkman to bring an internal conflict with Storm: who she was before Beast's death, and who she is now.
Xavier, on the other hand, should stay dead. He was masterminding a number of seedy activities all under the cover of the X-Men. There's the distinct feeling that the X-Men themselves were never in control of their mission, that they were just pawns in Xavier's blueprint for the future. Then Xavier got a glimpse at Cable and he saw exactly the sort of future his plans were leading to. He steps right into Cable's trap so that the youth will be able to plan the future without his manipulations. But the wheels are still turning, and the X-Men will have to face the groundwork that's already been set by Xavier to insure a happy future. I like them in charge of their own destinies, and that's something that can only be managed with Xavier out of the picture.