I suspect when Mummy closes--it closes properly and becomes a brand new darkcoaster.
The ride has been operating as it was since it opened in 2004--and has seemingly had no form of any notable retracking. Considering how frequent and often the ride has been operated for the past decade and nearing a half by 2027 (as by 2028, it would be operating for 14 years), I suspect they'd be treating this like a Hulk scenario where they're gonna have to replace a lot of the track.
This is likely nearing the point where a larger question has to come apparent for how much is worth keeping the existing attraction, or to just start from scratch altogether. And if I was UDX--I'd be highly considering the options for developing a coaster that can replace the current one, and to have it ready as soon as you can.
An Intamin MDC, indoors and modernized, feels like the right kind of a replacement for Revenge of The Mummy. Hagrids doesn't seem sustainable for the Hollywood park due to the lack of space--but having a highly themed darkcoaster for families and young teenagers would be a good option to compliment it from Hippogriff and Hollywood Drift.