http://tv.yahoo.com/blogs/tv-news/marcia-wallace--star-of--the-simpsons--and--the-bob-newhart-show---dies-at-age-70-154712041.html

Found out that Marcia Wallace (the actress who played Bart Simpson's Teacher) passed away. Looks like Edna will be retired from the show unless they find someone else to voice her.

It sounds from the short blurb by Al Jean that they plan on retiring the character rather than trying to find another voice actor. I've never been a Simpsons watcher, but the show definitely has made its impact on American society.