Gary Dourdan, who plays Warrick Brown, is leaving CSI at the end of this season. Remember Jorja Fox, who played Sara Sidle, left late last year. Both want to pursue other projects. I don't blame them. They've been acting on the same show for over eight seasons now; and playing the same character over and over again is not only tedious but boring. Even Barry Pederson, who plays Gil Grissom, signed on for another season, but will appear only in a handful of episodes.
For me, it's a sign that the show has run its course - creatively. But like the Law & Order franchise, CSI is a show where the process is the star, and the characters are secondary. So there's a good chance CSI will last beyond its original shelf life.