Yeah, sad to see the ending, it was very Sopranos-ish to me, and it was weird also, since we never see the core group "socializing" at the diner like that... Not sure how accurate this blog post is, but it's saying the actor himself did not want to renew his CSI contract:
Actor Gary Dourdan, who plays Warrick Brown on CSI, is reportedly leaving after his contract expires in May. According to TVGuide.com's Michael Ausiello, Dourdan already told producers he will not renew the contract.
Is 'Warrick' leaving CSI? ~ Pop Culture Madness Blog Celebrity News and Gossip
If anyone watches CSI: Miami, they similarly killed off the character of Tim Spedle in an episode a few years ago. He did come back and make a guest appearance either this past season or the season before as a "ghost" that another of the characters kept seeing...