CBS finally bothered to pick an official date, or at least give one to TV Guide. The press release should come out any day now, but TV Guide is citable confirmation to what everyone's sources have been saying. Billy Petersen's last CSI as a regular, One to Go, will air on January 15th, 2009. This is when we last expect to see Jorja as Sara Sidle.
Mild spoilers (more like hints) behind the link for what's to come. No mention of Sara.
As much as I want to see a happy GSR, running off into the sunset ending, I feel sad that this is the last time we are going to see Jorja on CSI. It's bittersweet indeed