Little Mermaid is fine the way it is. The last time I was there a couple years ago the theatre was filled to the brim. Not sure about the "lack of interest" accusation there. It still seems popular.
And honestly, this is a movie that has withstood the test of time. 1989 is 22 years ago and it is still a very popular attraction. I can think of a bunch of Disney movies that I would dread seeing go in its place. Mermaid is still a very immersive show.
As for Beauty and the Beast, honestly, how is this a show that needs the axe? Again, this is a classic movie 20 years old. It is the closest thing you'll see to a Broadway musical and the place is packed whenever the shows are playing.
The difference between Disney and pretty much everything else in the world is that they don't usually fall into the trap of gushing over the flavour of the month every time. Their movies and attractions age well and cross generations.
These are two very good attractions, with two very good stories. They're fine.