IMHO?

If the *main* imaginary characters were gone (Ed, Coco, Wilt, Bloo) I doubt I would, for it was those four that got me into the show to begin with.

Frankie and Mac are of course irreplaceable!

The rest are pretty much disposable, although guest appearances by Cheese, Terrence or Goo are always welcome...and anything that has Duchess in it!

I would not watch the show without Bloo in every episode, period.

Madame Foster and Mr. Herriman are as well. The former was the very founder of the house, grandmother of the caretaker and creator of the House President; the latter is the obligatory "stern authority figure" who provides humor through both his reactions to the silly antics of everybody else, and through HIS own unexpected silly antics. They may have been somewhat reduced in role recently in the new episodes, but they're still equally important.

Like I said, I view the entire cast as an ensemble, with Mac and Bloo being on a slightly higher pedestal than the others due to their status as the main, first-tier, "must be in every single episode" characters.

Yes. No doubt.