Grissom's involvement has been decreasing over the last few seasons. I feel like there have been quite a few episodes where he was in his office most of the time, or just running one test here or there. I do think the show can survive without him--the episodes with Liev Schrieber the season before last did okay in the ratings. I could be wrong, though, and let's face it--the show is going into it's ninth season. It's not going to last forever, though I have to say, it's still the number two drama or something like that (Desperate Housewives edged it out this past season), which is pretty impressive.