I don't mean this in a rude sense, but honestly, asking if the Muppets are still popular is like asking if people still drink Coke.
Yes the Muppets were probably way more hot in the 70s and early 80s, than maybe they are today in some regards. But characters like the Muppets, and I'll even though in characters like Superman, Batman, Spider-man, Looney Tunes, Mickey Mouse and Peanuts, have become pop culture icons. Even if Muppets Most Wanted didn't exactly wow at the box office and the prime time TV show only lasted one season with diminishing ratings, Kermit, Miss. Piggy and the rest of the gang still hold and will always hold a place in many people's hearts and will continue for many years to come. After all, that's a BIG reason Disney wanted to buy them in the first place.
One thing that's a pet peeve of mine is when people throw around words, one of this words is the word: "fad." One great example is when people try to say Pokemon was a "fad from the 90s." Totally wrong. Sure maybe Pokemon isn't exactly as huge as it was in the late 90s, where it was insane huge, look like it was going to take over the world and those poor parents at the time couldn't go 20 minutes without seeing or hearing Pikachu. But Pokemon is still very popular and continues to reach out to younger fans that weren't even born during the high of the Pokemon craze. That's NOT a "fad." Fads don't stay consistently popular for 20+ years. Fads last a year, TOPS, like kids wearing all their clothes backwards when the kid group "Kris Kross" made it popular for a short time or something along those lines. Same thing with the Muppets, even though people might not be beating each other up to get the latest Kermit the frog doll, that doesn't mean they're no longer popular.