I as well am perpetually concerned about video game preservation, but WoW is a poor example. Issues of copyright aside, MMOs in general just aren't the sort of games that can be capably experienced in a historical capacity. To use the obvious example, Nostalrius existed not out of historical curiosity, but out of nostalgic sentiment which is only going to continue waning. Even with access to the source, someone fifty years from now is going to have a hard time pulling together forty people (or eighty, if you want to do PVP) and convincing them to play a game together for months on end solely in order to experience a meagre facsimile of what WoW was like at its peak. (Though I'm amused at the prospect of a professional video game historian offering work-study jobs to history students that consist solely of playing a sixty year-old video game).

This sort of thing has implications for game design as well. If you care about your game being experienced half a century from now (which, to be fair, you probably don't), then you should attempt to provide an "offline mode"--even for games with online multiplayer--that makes a best-effort attempt to convey the spirit of the game. Dark Souls does an excellent job at this: even though much of the fun of the game is in playing online (seeing the hints that others have left on the ground, summoning allies for boss battles, fighting off invading players, seeing the ghosts of other players running around the level and the bloodstains they leave when they die), it also goes to great lengths to cater to offline players: there exists a spell that will cause developer-written messages to appear, there are summonable NPC allies and NPC invaders, all PVP reward items can technically (and laboriously) be farmed from enemy drops, etc.