OK, I can see it if the shows' writers wanted to try something different, but suggesting that a VOs wanting out alone is a valid enough excuse to kill or write off the character that they voice? Sorry, but I just think that's stupid. I could see it if it were a major character like Dan Castellenetta (Homer) or Julie Kavner (Marge), but why should the writers create all this death drama for a mere supporting character like Ned Flanders when it would have been so much easier to just hire a new Maude? When Janet Hubert Whitten quit The Fresh Prince of Bel Air, the writers didn't kill off Aunt Viv, they simply hired Daphne Maxwell Reed to take her place. Same deal when Dick York left Bewitched. Would you have preferred it if the producers had killed of Darren and made Samantha Stevens a widow instead of simply hiring Dick Seargent to to be the new Darren? I realize that I've drifted into live action here, but it's the same principle.
If anything, cartoon characters are even easier to replace because the audience is only hearing the voices. They have no idea what the actors playing them look like. All the producers would need to do is find another actor/actress with a similar sounding voice and move on. Should Jim Henson studios have simply shut down after Jim passed away?
As a cartoonist myself, I would only advocate killing off a character if it artistically validates me to do so. There's no bloomin' onion way I'm going to kill or write off one of my own creations just because the voice actor decides that he/she doesn't want to speak for him/her anymore. If I don't want my character to die or to be written off of the show, it's not going to happen. Period.