De Gea won't be frozen out. They purposefully fucked up this transfer to ensure he stays. It'll just be like Suarez post the Arsenal flirtations. In fact, I wouldn't be surprised if he signs a contract with a buy-out clause just like Suarez did, so Utd ensure they make a bit of money, and De Gea gets a pay day for staying the season.
The only question is whether this affects him mentally. It did the opposite with Suarez. When Ronaldo was initially denied a move to Madrid, his form didn't drop either. Only case I can think of in recent times where a player's form DID drop, is Sterling during the City flirtations.
I have a feeling this whole saga won't make much of a difference to anything, other than highlighting in front of the world that Utd are no longer in the top echelon of clubs aka Real/Barca/Bayern. Even PSG, Chelsea and City have a stronger pull factor than them now, and are routinely embarrassing them in the transfer market.
It's another sign that they have the potential of becoming what we did in the early 90s.
Would be amusing if he picked up an injury and was benched for most of the season anyway. Very amusing.