I was thinking about this, and surely they could take the majority of classes there? Ok, not Charms or Transfiguration, but presumably Potions, History of Magic, Care of Magical Creatures, Herbology, Ancient Runes and Astronomy could be done, maybe with some minor adjustments?
It doesn't seem like adult wizards do magic all the time either, and a lot the 'everyday' magic they use, they don't actually cast themselves (floo powder for example). I don't think you have to be magic to ride a broomstick either.
So surely they should at least have the chance to go to Hogwarts (and follow a slightly altered curriculum) rather than have to integrate into the Muggle community?