Educated guess: I think the Mummy will close right after HHN next year. They need that capacity for Summer ops and they really need that capacity and thrill ride for HHN. I think that will be “close enough” to the opening of F&F so they can get a head start on whatever is going there and get by with only a few months of not having a “real” coaster in the park.
I’m leaning a bit more towards Mummy leaving sooner than later (And by sooner I mean when F&F is ready to go) as I firmly believe that will be our 2028 major addition.
I do think the Simpsons contract expiring in 2028 is sucky timing as they will have to shut down a lot of that area to retheme it, but that’s a major artery of the park. They need that extra space for the Olympics.