I would like for somebody on the show to come up with an explanation for what happened to 456 SS and the people that work and live there, an entire block of the street just disappears out of the middle of nowhere, but I guess that makes sense, seeing as it appeared out of nowhere.
On the hurricane episode, Big Bird even remembers back to when that part of the street existed, even though it wasn't there at the time. He even mentions Ruthie, even though she wasn't on the show at that time either.
This is something I like to prefer to as the Sesame Matrix or the Sesa Matrix if you will. Any time someone or something disappears form the show without any explanation, It as fallen or disappeared into the Sesa matrix
Another theory is that the Amazing Mumford is making people magically disappear one by one, of that they all fell into Oscar's trash can to the point of no return, or better yet, it's all just a part of Elmo's plan where he is holding captives hostage in ordered to have the show occupied for a solid hour devoted to only to himself, and he's not telling a sole about it. To be continued?