Jorja Fox might be returning, but William Petersen is leaving, according to Yahoo!News:

“My biggest problem with leaving the show at any point isn’t leaving Grissom,” said Petersen, whose previous leave of absence came when he took five weeks off to do theater in Rhode Island. “I’m an actor, it’s time to do other things.”

Honestly, the only reason I watched CSI for as long as I did was Grissom. Willows isn’t as steady a character, sometimes she’s on and I like her, other times she’s useless and over emotional. I don’t think the writers ever really got into a solid groove of who Willows was. So I don’t think she can carry the series, and adding a new character to helm the show could very easily backfire.

I don’t think the show can quite be the same without him, but I’m sure people have said the same about every cast change on Law and Order and none of those have ruined the franchise yet.

Also in the article is the news that William Friedkin will be directing the series 200th episode. That should be interesting