He's had a dip in form, dropped a few clangers recently. Happens even to the best and if the Man Utd management team have anything about them, they'll recognise that's what it is and stay with arguably the best keeper in the world.
However, if that dip in form is due to other issues and he's not happy there or has had his head turned by the Real interest, they should get rid. They are a good club for promoting youngsters through their ranks, but rarely do they do that with a keeper. My guess is that if any movement happens, De Gea will go to Madrid and they will go for either Courtois or Oblak. The key for us is whether Romeo who is a good keeper in his own right is happy to be number 2 yet again or wants to move on and be playing more. If he does they may want Henderson as number two, again unlikely as that position is one they like to have experience. I think Henderson will either be loaned back to us for another season, or a transfer is agreed with a buy back option for Man Utd.