I will start by saying WoW is not going to die anytime soon.
Now, I have been a player for 7 years, but to me the game is dwindling heavily. I don't play it like I used to. I get bored quicker, to be honest I have grown tired and to me, it is dull.
that being said, personal opinions aside...
To say WoW's gameplay, graphics, etc are better than other games is just ignorant. There is only 1 thing that WoW excels, and it is in reality the only thing that matters in an MMO - the player community.
Warcraft has, 11 million players currently? It could fare to lose what, 9 or 10 million of those and still be competitive compared to other MMOs. People play WoW because everyone else plays it. Your friends, your co-workers, classmates, neighbors, garbage man, pool cleaning guy, hell your grandpa and his shuffleboard team probably play it too.
Lets look back at the last time a great, well established MMO died. Everquest, which itself was killed by the up and coming WoW.
What has to be made to cause people to leave WoW, and for WoW to die, is a choice of quality that surpasses that of the established community. For EQ, this was achieved by EQ2.
EQ2 and WoW both released in November of 2004. EQ was one of the largest MMO's at the time, but stopping development of EQ, and creating EQ2 gave people a chance to try something new. It was a reason for everyone to drop what they were doing and search for the next best thing. had EQ never released EQ2, I am willing to bet it would have gone somewhat differently. They tried to move their entire userbase to a new game, and in doing so their userbase found a home somewhere else.
Lets face it, in its early months, Warcraft was an absolutely horrifying game. the amount of gamebreaking bugs, glitches, imbalance, poor itemization, entire talent trees rendered completely useless, WoW in the first year was a practical abomination to the MMO industry. But they hit the nail on the head with a picture perfect release date, landed it in a time where because of the shift EQ made, there was no greener pasture to go to.
slowly perfecting their gameplay, WoW has locked themselves in as the absolute go-to titan of MMOs. The only way this can be killed is that quality decision stated earlier, and the decision is going to have to be MASSIVE to beat 11 million players. it would have to be massive to beat half of that.
TL;DR - The only way WoW can die is halting production on WoW for a sequel (lets say, WoW2), which will never happen. Ever. Blizzard knows how huge of a mistake this would be, considering they themselves dismantled Everquest as a direct result of this. You have many many MANY years to go before WoW can die. I wouldn't hold your breath. anyone who can blatantly claim the death of wow is seriously butthurt about something, but I guarantee that something isn't even remotely detrimental to the longevity of their IP.