You'll have to wait many years for that. The cow is noticeably thinner, but by no means dry just yet. They'll keep milking it!
I'm sure there will be one, but it'll take quite a while for WoW to die like that
The end of the Wow Beta was pretty fun; giant elementals (raid boss size) attacked the major cities, most people weren't beyond level 20 and I'd certainly seen nothing like it before. Of course we couldnt make a dent in them but it was a unique (at the time) experience, well done Blizzard.