Not a fan of this attitude, of course we don't have three or four world class players waiting on the bench for Rooney to depart - pretty much no club does, and United least of all because that isn't how we do things.
What we do have is three brilliant young attackers who could all go on to become world class. Kagawa has already proved it in Germany, for one. If Rooney were to leave and Hernandez started to get more game time there's nothing stopping him from becoming a world class player. He's already a world class goalscorer and the strides he made last year in his general play (which already proved huge sections of the Caf wrong) demonstrated that he can develop into a more rounded footballer.
As a fan of United you surely know that you need to develop players to help them become world class. We rarely ever pay huge transfer fees for our best players but develop them ourselves, which is exactly what will happen if Rooney leaves.
It's actually a benefit of him leaving to me, because if he doesn't I could see both Hernandez and Welbeck stalling and getting as little game time as they did last season, or in Welbeck's case having to play on the wing again.