If the club/new manager wants to sell him, then he'll probably go.
However, one thing about SI is that he's not the type of player to move on simply chasing a higher pay packet. He actually likes it at Villa. He likes it more now than he did 12 months ago, probably because he's playing football in exchange for wages. He wants to do well here, he feels like he's turned a corner (in terms of form and his relationship with supporters) and he doesn't feel the need to move on. If a new manager has other ideas, he'll try to earn his right to stay. He definitely definitely won't spit the dummy out if he isn't picked for the team, as you'll have seen this season. Wasn't in the team, worked hard in training to earn his right to play and then played well when given the chance.
He also feels he has a good relationship with the RL/PF in the aftermath of the Houllier debacle and is enjoying feeling part of the club.