I do too *cries in hands* William left because he wanted to pursuit the theater, which is his passion. I hope and pray that he returns to CSI, because I hate theater, no offense to him of course.
The show is going downhill (at least for me) and in some seasons lots of fans will feel that way and start abandon the show. The producers of course don't want to see that happening so they will bring back Grissom and all the old fans will come back running immediately.