I may be wrong, but they may have something in the Contract that causes issues if Shrek were to be removed. And also, It underwent a massive overhaul of its exterior line, received major changes to the theater in many ways; and added a full on Mural onto the building's side facing WWoHP. If anything, I would expect Shrek 4D to be staying around for a long time, much like Waterworld and the refurbishment from 2014 (and the massive 2017 refurbishment which could give more to the life-span of the IP's stay at the park).