George and Eric have both said time and again that they plan to stay with the show until the end, or as long as the show will have them. So I think THAT is why they signed on. They both love working on the show and love their characters.
As for Jorja, we still don't know for 100% whether she's going to be a regular again (in every episode) or on special guest star recurring like she was last season. But I'm sure that at least a big portion of the reason that she returned is because she loves the show and her character and she has left before, so she knows how much she'd miss everyone and the character if she left again.
Eric (like Wally) has MANY other projects outside of CSI that he does. He's also had starring roles in several movies. They may not be big blockbuster movies, but if he does any in the future, once his diehard fans find out about it, they'll be right there. If its a straight to video movie, it'll make a lot of money off his fans who've followed his career from CSI. I'm not the least bit worried about him. I have a ton of faith in him. I'm sure he'll be fine. I'm sure they'll all be fine. Their fans will follow their careers wherever they may lead most likely. And whatever they do, they will bring in many fans.
One thing I have been wondering about for a while is why everyones contracts are maximum 1 year long? Or has anyone signed a multi year contract? Could that be a sign that the show is coming to an end in the next year or so?
Contract deals usually have a time limit on them because people are never sure how long the show will last... and if an actor signed on to a network for their current show for say, four years and the show didn't last that long, they would still be in contract with that network and would most likely not be allowed (legally) to work outside of that network (at least not without the network's permission). So this is why they always renegotiate their contracts after they expire. Every show does this. It really does not mean much. So people re-sign most of the time because they love the show/character that they are doing. Or just even out of loyalty of what has made them more successful. I wouldn't read anything more into it. It really doesn't mean much more than that.
As for the length of contracts meaning the end is coming soon, I can't say for sure... but I think maybe the network realizes that this show has been around for a long time and there is no way to predict just how much longer it will last. It could go as long as 15 seasons like ER did, or it could drop so bad in the ratings at the end of this coming season that they'd be force to cancel it. One just never knows, so they play it safe lol. Although Ann Donahue, the show-runner from CSI: Miami signed a four year contract recently. I honestly am not sure if CSI: Miami would last that much longer, so her contract may be with CBS in general, so that when Miami ends she could produce or be the show-runner for another CBS show.