On the other hand a game’s “purpose” (I am hoping to avoid any sort of artistic debate here, so maybe I should say the reason the average person plays a game) is to provide entertainment for the user.

So in that sense for a MMO to “continue functioning well” requires it to continue providing new content for the player.

If someone says, “Oh, man, I just killed a mjork in the blue fjord,” everyone else goes, “yeah, yeah. I can do that, too.” But if the blue fjord sank into the ocean, then your story of the mjork is special.

Of course, you’d have to have gameplay that likes narratives…