I will not hold my breath on that.... Why would he not want to carry on? This will be probably be his last job. Whenever he decides to leave, his early successes (on the pitch) would have been a distant memory and I suppose the new guy would not be weighed down by that. Fergie was unique, and anyone coming after him would struggle.
He normally signs a two year extension but his last contract was a three year one. I have a suspicion that it's his last contract. He will be 68 (I think) when this contract is up and you can see he has aged in the last couple of years. I think this contract was given with a longer length with the view to him retiring at the end of it.
I think he'll be given the full term of his contract unless we do ridiculously poorly and he will either retire completely or take on a less time consuming or ambassadorial role for the club. I also think we will be having discussions with his possible successor during his current contract (most likely with his input) and have something in place before wenger goes to ensure a smooth handover.
Our board are a cautious bunch and like to plan and take there time to get things right (or what they perceive to be right) and I think given the recent fortunes of other clubs after changing managers it'll be a process they take time with and do in an effective way. They are businessmen rather than people who will get all passionately caught up in the football and make rash decisions.