I read on Sky that Heinze's lawyers claim they have a letter from Gill stating that he can leave the club if they get an offer of at least 6.8M. Then this letter somehow made the rounds of the larger clubs in Europe.
Man U have not said the letter does not exist, but believe it does not overide his contract. They've also said he's already passed the deadline to buy out the remaining year on his contract. Sounds to me that's one for the lawyers to sort out.
However there are two sides of this if we look at it objectivly. One if he is really under contract (no get out of jail card) then Man U have every right to keep him. Why sign a multi year contract if your not going to hold both parties to it. From the players side, I also heard he's interested in playing for Liverpool. Got to assume that means he wants to stay in England, wants Champions league football, and wants a team where he thinks he can make the starting 11. For a player who just wants to play, that makes perfect sense. He may also think we are odds on favorite to win the champions league next season, which is one major compition he's not won (I think).
However bottom line, unless Rafa is trying to prove a point, not sure we need worry about this. Right now based on performance of Risse, Heinze would only get limited time at left back based on rotation policy.