I don't think he'll be off anywhere. He has the power here that he obviously lacked at Arsenal, he is allowed to run the club as he sees fit and it is working. He had his fingers burned before, I'd like to think he'll stick around. He's got a genuine chance to build a legacy with us and go down as a Villa legend.
He's surely rich enough to go "right, I'm doing well here. They love me, it's going great and I could go down as a hero. Extra £££ from United won't mean much to me, a man in my position in the long run". Managers can work into their 70s, so unlike players money doesn't HAVE to drive everything once you're at the top I'd assume.
We are going places whereas United et al are living off past glories that mean less and less as time goes on, as well as being propped up as "still a major player in the league" by the likes of Sky.