Not convinced at all that Disney envisions The Simpsons in their parks. Outside of Runaway Railroad and the Splash Mountain re-do, the priority for Disney parks is very obviously Marvel, Star Wars and Pixar.
The fact of the matter is arranging some sort of licensing deal is a cost and resource saver for both organizations that allows them to move forward with higher priorities for their parks. Were it not for the Fox/Disney merger, we're not having the convo -- there's never been any indication Universal wants to ditch this property. And again, unless it's Marvel, Star Wars or Pixar, it's probably not part of Disney's future plans (immediate or long term); their margins are thin and getting thinner, I don't see them sinking more money into developing Simpsons stuff for parks when they can just cash Universal's licensing fee.
Unless Disney decides to be stubborn about it (which is highly possible), I think Simpsons remains at Universal Studios for a good long while.