I have to agree with other posters. They will be around for a long time. They are a niche religion and there will always be personality types that will fit it quite well.
If the GB got up tomorrow and said right out "We are a sham", someone below them would cut/paste a bunch of scriptures to show that this was part of prophecy and ret-con their history again, etc. My mother and the rest of my family would buy it as they are so invested that they will ride this bus all the way down the precipice.
I have day dreams where I get to see my family again. But it is just that. I am pretty much resolved to the idea that I will not get to see any of them or for that matter bury my own mother when the time comes.