Re: Twelth doctor cast?
I would hope he sticks around for next year's series (whatever that may be). If they do Regen him early it'll be quite a shock. I wonder if they might do something unprecedented... and completely surprise us. Remember, people actually thought in the Stolen Earth Cliffhanger that we were going to lose Tennant Early. In some ways that could have been awesome, though it would have robbed us of his rather fantastic actual regeneration in End of Time.
I'm being extremely clever up here and there's no one to stand around looking impressed, what's the point in having you all? - The Doctor, interrupting a very important conversation.