Well, I left WoW for FFXI, and I don't think I'm a complete rarity in that sense. As a WoW player (well, sort of, I guess, my subscription is still valid for six more days) seeing numbers like 500,000 is kind of mind-blowingly small when I think about how Blizzard was all "Hey guys, we have 10 millions as of this holiday season!" back in January.

That being said, I think that any MMO can pretty much last forever. Note EQ.