At the end of the episode, which had already been produced months ago and had nothing to do with Mrs. Krabappel, they showed a still frame of Mrs.K. sitting on her desk with "In loving memory to Marcia Wallace written beside her. The frame becomes animated long enough for her to give us her trademark laugh of "HA!"
As a major fan and collector of Simpsons memorabilia, I am going to miss her character, who, after seeing on the show for 25 years, seemed almost real to me and many others who took to the Simpsons facebook page after the show had aired.