I have a mental hangup with the very real dread of when hosted multiplayer games die, that all the time and effort I have spent, and all the things I've built, will just suddenly disappear. It's why I run a private G17 Mabinogi server on my pc, rather than playing online.
Saw this trailer the other day that might interest you, it's an offline type mmo where all the other players are simulated. Erenshor Offline MMO Trailer