I think outside some specific circles (like here) the blowback from closing Muppets will be rather small. Just like removing GMR there will be a lot of concerned diehard park fans, it'll generate some noise on discussion boards, but the vast majority of park visitors will be completely oblivious to it, and just wont care. Given it's Muppets, there will be some small news stories, the morning shows will mention it in passing but will couple it with a message of "Disney is bringing in an exciting attraction featuring Monsters Inc which we all know and love". Disney will do some sort media thing to honor the Muppets or Jim Henson's legacy to placate the fandom, and give the illusion they care about them and the property, and then quickly pivot to fluff pieces showing construction updates with attractive people in hardhats building ground.
Conversations will quickly move to how its progressing, and repeat park visitors will say something like "oh yeah, there used to be some sort of Muppets thing here." Similar to how people discuss Dreamflight and the old Norway ride. This isn't IASM, it's not a cultural icon.
Edit: I was going to change "will be" to "would be" but the more I thought about it, I'm leaving it. Muppets is on borrowed time, if it's not now, it's soon. They've tried several things to revive the IP and results were not promising, and they've tried to invest in this area of the park only to see it still struggle. Something will happen here, this park is too landlocked for them to not use the space more productively. Sorry to Muppet fans, I don't mean to be cold, just speaking the truth from a business perspective.