I think fundamentalist religion is about getting away from reality. As a therapist you might almost see it as a rather successful way for those struggling with poor mental health to actually move through life in this complex world. The delusion is a coping strategy for them. Those born into it often leave battered and bruised but essentially they escape because they are well. It's being around the deluded that is harming them.
Personally I don't think there will be mass suicide because they share a group delusion that keeps them going. They will just decide it will not be in their lifetime after all. From my JW friend who has been in for 60 years I gather those that remain think it is the best way of life possible so even if the promised bliss is a long time coming they feel protected and safe.