I was wondering, how would we be able to document MMOs that are already defunct and haven't been added to Mobygames at the time of its prosperity. I just feel sad for the online games that are lost in time, and clearly cannot be played anymore unlike many other classic offline games.
Look at how we documented Habitat or Dark Sun Online, two MMOs that were defunct well before we hit the scene. If you don't have all the details, you can only document /some/ of the details -- eg. box art but no screenshots. Press releases and old guild pages on Geocities help 8)
I deal with such problems when I decide to make entries for games on old online services like Compuserve, Prodigy or GEnie. You just gather as much data as you can.
BBS door games are in a similar pickle, though often they can be downloaded and run locally. (Some, like games for the influential MajorBBS system, require a working BBS to be part of. Which is why the first Kyrandia game isn't documented here yet.)
Even though I don't personally play MMOs and I rarely play any form of multiplayer, I've wondered the same myself.
It seems to me that of all games, MMOs get the worst deal. Even if copies of the game and the machines needed to run them survive the ages, at some point or another someone pulls the plug on the official servers and then the game is basically 'dead'. I haven't exactly looked into it, but I suppose there may be some MMOs (or perhaps MUDs) that have survived through unofficial or pirate servers. That would be a funny way to save a game from 'extinction' - Internet piracy. It's obvious that a game like World of Warcraft, with still huge fanbase, would survive through such servers; but what about others?
Another thing I've wondered about is what will happen to the many current single player games that also rely on Internet services to work if and when those Internet services stops. How many developers will bother or will be around long enough to release some sort of 'patch' that allows the game to survive in the absence of that service?
But I'm off topic, aren't I?
Downloadable MMOs are still relatively safe since they can be cracked in the future. Browser games are in the worst situation, frankly.