Actually, knowing his relationship with Rubens + the fact that Barrichello will very likely be racing in IndyCar, it wouldn’t surprise me to see Mark follow him. He doesn’t really have many options left in F1.
Red Bull
His relationship with Vettel&the team and his performance last year kind of guarantees that he won’t stick around for much longer. Buemi, Ricciardo and (highly unlikely) Hamilton all seem like better options.
McLaren
This one seems surprisingly plausible. I don’t see Lewis sticking around after 2012 and I can’t think of any realistic replacements for him. Still not too likely, but I can see him doing that in order to spite Seb. It’s not up to him, though…
Ferrari
“This is your captain, Fernando, speaking. Your flight is ready, mr Webber”.
Didn’t Alonso say something like that when he called Mark to remind him of the awarding ceremony? Maybe their relationship is closer than one might think. It’s not smooth sailing, though. Webber does not like playing second fiddle for anyone, and Ferrari is all about that. Plus, they have Kubica, Bianchi, Perez (and a couple of others whom I’m likely forgetting) on the list, all of which would be better for the team.
Mercedes
Only if MSC retires and if they somehow manage to win any races, which, according to Brawn, is unlikely. And even if that happens, Di Resta would be a better replacement for Schuey.
Lotus
Only if they continue the pace they seemed to set in the first test, which isn’t too likely to happen. If the team messes up and Kimi leaves, Webber won’t want to join them anyway (midfield team, *ahem*), but he could possibly replace GGGGRRRRSSSSJJJJNNNN.
All in all, there’s not much hope for him.