Regardless of whether it's remotely feasible (which it probably isn't), just as a hypothetical, I'd welcome him back with open arms. I'm well aware of what he did but I for one can let it go. Would have a few advantages:
1) Obviously he's good at football so that would help. We can't afford a striker of his quality -- we can't even afford a young striker with the potential to be as good as him.
2) The sky 4 media would probably [Poor language removed] themselves in disbelief that someone would choose us over a "traditional" CL team (hopefully we will be a CL team by then). Would also perhaps send a message to young players that the grass isn't always greener. If we still have Rodwell, might help him decide to not bother leaving when a player of that quality is coming back.
3) Be kind of funny if that "once a blue always a blue" thing turned out to be true after all.
That said ... can't see it now.
You know how these players always say [Poor language removed] like "I was looking for a new challenge" when they move clubs? Only they're moving to Barcelona or Madrid ... how much of a challenge is it to win things with teams like Barca? If he really wants a challenge, coming here and turning us into a contender would make him far more of a legend (not just with us but as a footballer in general) than being one small part of the continuous winning machines at these other clubs.