United are trapped by their own folie de grandeur. They need to forget all the shit like "biggest club in the world" and "United way" and go away for two or three years - in effect - not bothering about league position or winning owt, just focusing completely on rebuilding the club from top to bottom. They have got the financial resources, and they have (probably) got some decent lads in the youth team. They need a Director of Football for sure, but that's just a start. The whole set-up in rotten and needs reconstruction. It would probably help if Ferguson and Charlton buggered off, or at least took the Trappist approach for a bit.
The problem is the fans - and quite likely the owners - would not like the consequences of this, because for 3-5 years they would not be able the play the Big I Am and would in effect be settling for a degree of short-term mediocrity.
The other snag is finding the people (Manager and background staff) to execute the rebuild. Very, very tough. Because the guys with the right qualities are few and far between.