He will re-discover his form. If he goes and UTD don't replace him then they will struggle if and when RVP gets injured which is inevitable with Dinosaur Moyes and his methods!
Suspect this is why Utd want to keep Rooney so much.
As mad as it is, they probably wouldnt be able to replace him for the £30m(ish) they'd get for him. So many strikers have moved this window already. Who's left? Not only that but Van Persie is so clearly their number 1 striker. So you can even sell the aspect of being Utd's no9.
Also agree that he'd rediscover his form should he leave. He'd have a point to prove and seems the sort to carry a grudge. He'll be desperate to prove he's still got it. And Chelsea would be an ideal environment for him. Mourinho would play to his ego to the nth degree.
Has some parallels with our Arsenal/Suarez situation.
Utd wont be able to replace his quality and they'd be directly strengthening a rival. No wonder they're fighting it.