I've seen this debated elsewhere as to whether or not the characters make CSI or if the stories make the show.
In CSI's case, for me at least the characters make the show. I like them all, though to be honest Sara doesn't do much for me. To the above post which mentioned it, yes, she was caught drinking and driving in the final ep of last season, so her story is obvious. Nick on the other hand I liked. I would guess if they decide to mention why he's gone, it would be for a promotion somewhere else.
CSI Miami however I watch because of the stories. I could care less if they get rid of any of them except Cali, I like her.