Death of the hobby? No way.
Death of the industry? Ten years ago, I would have said 'probably'. Now, though, I'm not so sure. The explosion of PDF, PoD and Kickstarter means that there are all sorts of ways of attracting interest and getting product out there that don't require the existing distribution network, which probably does rely on D&D to keep it functional. It would be a decidedly different industry, but I'm no longer convinced that the downfall of D&D would reduce roleplaying to a self-supported hobby. More of a cottage industry than it already is, mind, but not completely devoid of professional or semi-professional product.