Outside of the entire Governing Body being indicted and convicted for some pretty horrible federal crimes of some sort, it's going to be hard to take down the organization with a direct hit. It's too big.
As has been mentioned, it can run out of gas, though. If the money stops pouring in or is no longer sufficient to support all of its members, you will see the Organization respond with something panicky, which should be a big red flag to anybody paying attention. Mandatory tithing, heavy suggestion that people leave their proprerty to the Organization instead of their own children, and things like that.
But I don't think that's likely to happen anytime soon.
Our best hope is disease or poison. Something has to spread throughout the Organization, and the internet is our best bet for that. Sites like this one and youtube are a huge help. It pleases my heart when I see an ex-JW or anti-JW or even questioning-JW video and it has several thousand hits. There is enough damaging and legitimate information out there about the WBTS that people don't have to make things up. People can't say "that's not true."
The only real hope the WBTS has right now, believe it or not, is young people. There are plenty of 40+ year old people dragging it on. Statistics already show that young people are flying out of the Truth like bats out of hell. At this rate, the Society has about 20 years of life left and then it will no longer be able to sustain itself, especially the congregations in the United States.
I am confident that the Organization won't last much longer than 20 years or so, at least not in its current state. There will be pockets and fragments here or there but we are witnessing now the beginning of the end. We are already seeing signs of desperation. I predict that next the Society will act in such a way that it encourages some kind of persecution. Witnesses like it when they are being persecuted. It makes them feel useful. I am anticipating there will be some new arrangement where we have to act in such a way that is opposed to some secular authority. It's coming. It will backfire. Hardcore people will just take the persecution, but more people will leave. Young people won't even bother.