I think Obama will not accept this spot, just as I know Hillary would not in the reverse. What is in it for him?
If she runs and loses (Not at all likely IMO) he’s around to pick up the pieces next time. If she wins, he’s not a part of the disaster that will surely follow.
Plus, he’s free to establish his own base and fill out his credentials. On the outside he would wield much more power than on the inside.
If she loses, he will certainly be the nominee in '12. If she wins, he will go from being a junior Senator to Vice President of the United States, not yet even fifty years old. Come on, it's obvious. The ticket is Clinton/Obama.