Mary Moo Cow would not be cancelled just because the woman in the cow costume quit. The producers would find a replacement.
Arthur and Buster: (singing to the tune of "Yankee Doodle") L-A-S-T. That spells "last." No more Mary Moo-Cow!
(in a dream, D.W. tries to play basketball on a dark, sad day, but the basketball deflates and comes alive)
D.W: Come on, we're supposed to have fun.
Basketball: Oh, what's fun about it?
Bike: Without Mary Moo-Cow...
Daisies: There's only Dark Bunny!
Everyone except D.W.: Bleahhhh!!!
D.W.: You're not Mary, you're the boring woman.
TV Game Show Host: Is that your final answer?
Mr. Ratburn's first name is given as Nigel here. In some past episodes it was thought to be Emil. It's Nigel Emil Ratburn.