[quote=Ace of Spades]
Pretty sure nobody will want to go through 15 hours each to catch enough Pokemon to gain access to Cerulean Cave and fight Mewtwo.
[/quote]

There's a Pokedex requirement to get inside Cerulean Cave?

Pretty sure you just had to clear the Elite Four.

At any rate, I'm sure there are SOME people who would want to keep going. And, yeah, some would leave - but that would just make things easier for those who stayed.