A short term fix imo would work if United were struggling for cash or they had numerous positions to fill.
The truth of the matter is United really have to fill/upgrade in two positions and they are ready to challenge again.
I really do see Sir Alex laying down the team for years to come on a platter for the next manager. The manager won't have massive changes to make. They can focus on the fixture list and not the transfer market.
That being said, in order for this to happen, United will continue with their youth policy. Would be shocked if a player over 26 comes to the club.
IF we could get a player like Henry who is under 26 great. Henry himself.

He has been a moaning diva at Barcelona.
I'll even toss in another player from Barcelona. Samuel Eto'o.
World Class striker whose playing style and strengths would perfectly complement Manchester United.
The fact that he has stated his desire to play in the Premiership along with his rumoured valuation [which still seems unbelievably low to me] of 15 million pounds would be ideal for United.
I'm sure a player exchange plus cash could work. Pique + cash for Eto'o. Barcelona really want Pique back and United would be getting a player that fills a direct need in return.
Note 1: My list has now increased to 3. Any of Huntelaar, Benzema or Eto'o would be just fine with me. The key is a striker that stilll has many years left to play, has European experience and can quickly settle into the swing of things.
Note 2: I'm a big Pique fan, but the question has to be asked. Where does he get games? Rio and Vidic are going to be holding down central defense for years to come. Rightback will probably addressed this summer and the defensive midfield spot is filled. Pique was fortunate enough to get 9 games this year. What are the chances he gets more next?