They've kind of written themselves into a corner. The only reason the school exists the way it does now is that once upon a time, Marvel decided to emulate the movie premise and kind of quadrupled the mutant population. After decimation, they could have gone back on this, but then they did AvX and undid the whole story repopulating Earth with mutants, thus re-uping on the student body. Again, they had a chance with T-mist, but that would have been a darker story than I think they were willing to tell. The X-Men can't just walk away from school as is. From a story standpoint, I think if the X-Men went back to being super heroes more than activist-educators, things would be more exciting and dynamic, especially being able to focus more on a couple core groups opposed, to those core groups and 3 dozen silly background characters. So no, unless they are willing to revisit a story like decimation or the T-mist, they shouldn't close the school. Not without the X-Men looking like ghouls.