I don't think its a full gone conclusion that he leaves this season but i do think its a full gone conclusion that he wont sign a new contract. So i think if he doesn't go now, he will go for free next season. Of course anything can happen in this transfer market and i would be delighted if i was wrong and he signed a new contract.
I highly doubt DDG would do that to the United fans if anything he'll sign a new 5 year contract and get sold for 30m