Was it so very brief?
For several years at least he was one of those unsung players whom Fergie could rely upon when facing top opposition like Arsenal or Chelsea. You also appear to be writing off last season as if those individual performances were a shambles from start to last, which doesn't square with the reaction on here IIRC.
Now maybe he doesn't start games for us much this season, but if he can secure enough minutes on the pitch to regain form then he can still be a calming force should we want someone to help us close out the game IMO [he seems to be a good organiser and possess some tactical awareness in that way].
I reckon on the whole, although of course not entirely his fault due to the illness, that he has been a poor player, by United standards anyway, for more time than he has been a good Manchester United player.
As far as loyalty from the club is concerned, he has gotten a great deal from the United. He's been with us more than 10 years, off the top of my head, I'd say he's had perhaps 2 good seasons, maybe 3, I don't know, and also spent a fair bit of time being quite some way off the requisite standard. When you consider the players that have left us in that time, he's been treated fantastically. If he were to join Hull or St. Mirren in January, he cannot leave feeling he's been done harshly here. As much as people hate the suggestion, I think it is clear that Fergie had felt some sort of particular loyalty towards him, certainly one that exceeded his talents.