Probably never, but if I had to put a date probably when Dan Castellaneta can't work anymore. So a while.

At the same time when world ends

Google will buy its rights and will force us to get a Google+ account in order to watch it.

That's when everyone will stop watching it.

yes!

Either when the world ends or when electricity runs out or when they run out of ideas or people demand it to end.

Probably never.