A couple of years ago I saw Richard Wilson play Malvolio at the RSC. For someone who is well over 70 he was remarkably sprightly and cavorted around the stage, so unless there is some medical suggestion of an underlying problem I would not take any bets on him for 2013.
He's showing no signs of slowing down, I'd wager he'll be around for a while yet
However I think his character of Gaius in Merlin will be dead before the end of November - This is a guess not a spoiler!