If you took the original voices of the Simpsons away...the series would die within a year. The thing about it....they make millions off the series and can afford to pay a pretty fair amount of money for the guys who do the voices. Why would you screw up a good thing?
As for Futurama? I’m betting it dissolves away within twelve months. No one will buy the last season in DVD form....and it’ll be one of those things....best forgotten.
The Simpsons’ golden era started a few years into the show and lasted quite a while. They jumped the shark a long time ago, though. Time to bring in Kazoo as a permanent character.