RPG's aren't going to die, or even strongly fade. They've got a certain generational strength that protects them. They can become popular, become a fad, but there is a distinct core there that will be through the ups and downs, and it recruits more gamers, slowly and steadily.
So not as many 12 year olds are learning D&D because they can plug in and play EQ? Well, it's only anecdotal evidence (but as has been said, that's all we've got now), but our college gaming club has recruited several dozen people into being gamers who had no interest or real knowledge of RPG's beforehand over the last few years. People who wander by a session in a dorm and wonder what's up, or roommates or girlfriends who get involved. Gamers have non-gamer friends, and they can be easy recruits. The average age of entrance rises, but that is just cultural evolution.
Also, I know there are gamers who game not because they discovered it themselves as adolescents or were taught by their friends in college, they were raised to it. One player in my game has gamed since childhood because her mom is a vintage OD&D player (circa 1975) and she was raised on 1e (and I get the honor of being her introduction to 3e today, since she refused 2e when it came out but wants in on the game that her daughter is enjoying).
As much as TSR, and later WotC have tried, you really can't teach D&D straight out of a box, at least not quickly nor easily. The method of recruitment and propagation for RPG's is interpersonal, friends recruit friends. It isn't highly efficient, but it is our way, and it does work. Should some horrible economic cataclysm happen and WotC fold, White Wolf collapse, and the RPG market go completely in the tank, those of us out there will still keep playing. Thanks to the permanent nature of the OGL & SRD's someone can even come along and resurrect D&D (with a different name) like a phoenix from the ashes. Even without that, it would be just a matter of time before more fans went out on a limb and started publishing their own games again. Getting it into bookstores and distibution chains doesn't mean as much when it's on the web for free and a worldwide network of people is recruiting and encouraging people to check it out.
We are a niche, a subculture, and while we can grow and expand, we should be aware that we aren't going to be "big time", even under the best of circumstances we can only grow so large. We should worry more about the quality of our games, the memberships of our gaming groups and clubs, and growing the hobby at the grassroots level instead of expecting any company to do it for us.