2. Population
Sadly enough, the end of civilization in these worlds comes down to one major factor: reproduction. The key to any healthy species is to reproduce effectively and efficiently. Our world today is so massively over-populated that our raw materials are resources are quickly drying out. On the other side of down, the entire population of an RPG could be overrun by the attendees at Comic Con. Most towns and even "big cities" have a dozen or so people that inhabit it - Final Fantasy XII being an exception. Sure everyone has space to do cartwheels, but at what cost? With so few people, reproduction is probably suffering as well and in turn makes human kind an endangered species. I guess you could argue that everyone gets a lot of action, but what that would eventually cause is inbreeding leading to low genetic diversity which in turn leads to people with no common sense, no law, and no reason to kill monsters. Oh wait....