I think he would as long as he has won his grand slam (PL, La Liga, Serie A and Portugese leagues), and is at a club where he feels he has much more control than he would get at any other option. Which I think is one of the two reasons he seems so set on coming to us, as he sees us giving him that control far more than any one else at a similar level. The other reason I think he wants to come to us is simply the ego boost to be 'the man who succeeds Ferguson'.
He'd still want to manage Portugal before he retires, but as long as he wins La Liga before coming here he'd have a good 15 years where he'd have no specific goals or aims taking him away.