I think "The Elder Scrolls: Online" will be the nail in the coffin for wow. Its just been around so long, I can't imagine it garnering much attention anymore. And while there have been competitors to it in the past, they haven't had the fan base to overcome blizzard.
However, that being said, if I'm not mistaken TES: Online will be completely free to play, unlike wow. Also Bethesda does indeed have the fan base to take them on, and personally Bethesda puts out far higher quality products than blizzard. Diablo 3 was a joke, not even worth releasing, with the marginal updates from diablo 2.
Sent from the stars...