It’s been almost a year since Marcia Wallace died (Oct.28, 2013).
And it’s the usual practice of The Simpsons staff to retire any characters voiced by someone who has died rather than find someone else to voice the character.
Marcia Wallace also played the secretary to Bob Newhart’s Psychiatrist character the entire time it was on the air.
Poor Ned is a widower again. That will probably become a running gag. As for Edna, I say spontanious combustion, which often happens with older alcoholic women.