No, the WTBTS will never fall. It has too many hardcore zombies at the center. It may shrink, but it will never fail to ensnare people every year.
It's not going anywhere anytime soon, because the people in it have their little blinders on and are running very hard in their exercise wheels, so they don't notice much that is happening in the outside world.
Besides, they have an army of millions of free book-sellers working their silly asses off in FS, and that's something no other religion has, really, it's a very strong point towards their continued survival.
NYT, I'm not even going to start...