Assuming he doesn’t totally mess up 2011, I don’t see why Webber shouldn’t still be here for 2012. He may have lost out on his best ever chance at the Championship in 2010, but he was still very close to Vettel.
If Webber WANTS to stay for 2012, and so long as he’s as good in 2011 as he was in 2010, I think Red Bull will keep him. I don’t see him moving teams though- I doubt he would want to move to a slower team, and I think McLaren and Ferrari would want someone younger.
So put it this way- I expect Red Bull will be the last team Webber drives for, but I think there’s a good chance of him still being here in 2012 (unless he doesn’t want to).