Even if we had been promoted, I don't beleive he would have come back.
I used to have a season ticket in the red seats (pre recession) and the last home game of that season, Sidwell was not selected, even on the bench so he was in the Exec club having lunch in a suit (non playing players had to still be at the ground for PR). I spoke to him then and he was mightly pissed off with the club for (a) not giving him the contract he deserved and (b) not picking him for the last match so he could say goodbye to the fans. This latter really seemed to mean a lot to him.
I doubt he needs the money now and in any event, we would have offered him much less than he's probably on now (the Madjeski way) so on financial grounds and bearing a grudge grounds, this is (IMHO) a non starter.