Professional dignity?
He could perhaps revive his career in Italy. However, if he has lost his love for the game then he'll probably just be happy to wait it out here and collect his wages without contributing much.
I think for everyone there's a limit of how much they'd be willing to give up to continue their career in a place they're wanted. He moved to United mainly because of money, otherwise he would have probably stayed at Arsenal or gone to City, so I'm not exactly sure he would be willing to take a pay cut to move somewhere else now.
It might not matter though, if he gets an offer from Italy that is 70 or 80 per cent what he makes here, he will probably take it, and if United are offered to offload him if they contribute 30% or so of his wages for the next two years, we will also agree to that I guess.