I'd be shocked if they took Mels or Hello Kitty... not after all the money and time spent renovating that store. They could easily swap out Kitty if sales were low, but wouldn't lose the entire structure.
The meet and greet for Transformers would likely stay and new building would carve out a spot to leave it there. The costumes are housed in the shed adjacent to Shrek, but not technically a part of the original building.
Some space must be left behind the old Shrek building though, as this is one of only two food service locations for Team Members in the park (unless that's changed since I worked there long ago.)