[TexasCajun]

The only one I remember being killed off for good was Ned Flanders' wife, Maude.

The Simpsons- Maude Flanders Death

But there are lots of other:

In-show deaths ...pets hardest hit.

[Vince Ferrer]

The only one I remember being killed off for good was Ned Flanders' wife, Maude.

That was because the voice actress wanted to leave the show.