I haven't really played any MMO for longer than about half an hour, so I can't comment with too much authority on whether they have win/loss conditions, although some like EVE seem from what I've heard to have a form of permadeath in the sense that it's possible to permanently lose ships, money, territory etc.
"A game is a system in which players engage in an artificial conflict, defined by rules, that results in a quantifiable outcome." -- Salen, Katie; Zimmerman, Eric (2003). Rules of Play: Game Design Fundamentals. MIT Press. p. 80. ISBN 0-262-24045-9.
I don't think you can have a quantifiable outcome without a game-over condition and some way to compare performance.
I'm not sure I agree with your interpretation of this; I don't think that you need to have reached a definite end-state before you can quantify outcomes; you can assess things which are still ongoing. Decisions in real life can have near-infinite strings of consequences stretching off into the far distant future, but we can still examine the outcomes of those decisions
at the current time - we don't need to wait for the heat-death of the universe before we can come to any conclusions about them.
So even if there is no hard 'game-over' state one way or another in an MMORPG there can still be present states which are more or less preferable and which depend on the actions of the player, the same as any other game. Even if goals are entirely player-set, constantly shifting and difficult to externally quantify those players will still
have those goals and act accordingly, so I don't see any real reason why we cannot analyse them in the same way that we would a more prescriptive game (beyond the additional practical difficulty of doing so).