They'll keep going for a while and then slowly decline until there are only a few thousand dubs. Then they'll establish communes where all dubs will live together and practice playing New System until they slowly die out...unless some enterprising young GB or Nephinum (or whatever they are called) seizes power and comes up with a whole new bunch of prophesies and directives from Jah and whips the dubs up into a viable money-making publishing house/pseudo-religion again.
Actually, I have no idea. I'd like to think the majority of JWs would eventually see what's going on and quit, but I doubt that will happen. People sometimes need a safe little box to live in. Sadly, I did too for a while. I don't see that ever completely changing.