That's a good question and one I've thought about over the years. I don't think it's going to end any time soon, but it could become a shadow of it's former self, at least in modern Western societies.
It seems to me the WT has to decide if it wants to be a mainstream, or even slightly odd fundamentalist religion, or remain a cult. Either way, it's going to have to start coming up with some new light and excuses pretty quick with 2014 on the horizon and no Armageddon in sight.
If it wants to mainstream, it might need to brace for a lot of defections. An earlier poster mentioned the Worldwide Church of God. They mainstreamed within a short amount of time, 10 or so years if I remember correctly. They ended up losing over half their members in the process. Of course, if the statistics are right, the WT loses over 60% of their membership anyway, so who knows how it would actually work out for them.
There's an interesting aspect to the WCG story. It turns out that there are some former members who want to go back to the old, nutty ideas about the end of the world, even predicting actual dates. They have advertized for former members, trying to pick up those who left the group. I don't know how successful they have been. I do find it interesting that there seems to be a market for this stuff among certain segments of the population.
If the WT wants to remain a cult, I think there are some natural limits for them. To try to maintain that kind of control over an organization and it's followers has to have its challenges. And while cults manage to attract some people, they will never become more than a fringe group that's easliy dismissed.
I would be surprised if they tried to pull a Jonestown. They are just too big and have been around too long to make that seem plausible to me. I also see no way in which that would be to their advantage, and at this stage of the game, everything the WT does is for its perceived advantage. Jonestown, and other similar situations, happen when there is a deranged leader that followers worship like a god. (I know what you're thinking, but the GB is still a group of mostly faceless men that the average JW wouldn't recognize if they passed on the street.) IMO if they were going to do something like that, they would have done it when Russell or Rutherford ran the show.
While the WT is similar to other odd groups and predatory religions, they also have their own unique situation. I guess we'll just have to watch and see what happens.