Keep him there till the end of the season, he's doing well and looks a top player in that league. His time at utd has unfortunately passed, we need a serious upgrade to the wingers we have (excluding Di Maria), we have a potential sale here that can bring us a decent return. As good as he has been, as a player in his prime years he is not good enough for us, we need better.
Other players like Lindegaard, Amos, Evans, Fletcher, Anderson, Cleverley, Young, Valencia, Hernandez need to go and be replace to an extent.
Young players like Johnstone, Thorpe, M.Keane, James, Vermijl, Powell, Zaha, Lingard, W.Keane should move on to better their careers. The only Young player on loan we should keep and invest time into is Henriquez.
A few players have ? Over their futures too, Blackett (is he really good enough), Mata (too high profile to be back up), Fellaini (Don't let a few performances fool you, with better players we won't need him).