This is supposed to be Desperate Housewives' last season and there are rumors that this may be the last season for Grey's Anatomy as well. It's likely that one of those shows may kill someone off. And I did hear a while back that even if this wasn't the last season of GA, that it would be the last season for Patrick Dempsey, so...
My guess would be it's a character from a more buzz-worthy show... GA is a good guess (I imagine DH will kill off at least one character in its final season). I can't see the value in CSI doing away with Nick (or any other character) right now, especially in the wake of Catherine's departure.
I watched the first video that previewed Catherine's goodbye. I've missed most of this season, but I think I'll try to tune in for her final two episodes!