I guess I just don't understand why certain rides have to be replaced every 20 years. I get that space is limited, but Disneyland has managed to keep even much older attractions around, so why can't Universal do the same? I don't see anyone expecting a replacement for Big Thunder Mountain, and it's been open for 40 years now. If parts are still available for it, Mummy should have parts available as well. Are people going to be calling for Hogsmeade and Diagon Alley to be replaced next decade also?
There are some attractions at USF that need to go imo (Shrek, Minions, FFL), but it's more because of quality and has nothing to do with the age.