One might compare Jehovah's Witnesses with other christian religions. Most christian religions teach there will be an "end of days" and teach of the rapture. This teaching has been taught for centuries, if not from the dawn of christianity. There doesn't seem to be a mass exodus from other christian religions.
Accord to the Watch Tower Society, Jesus began to rule in heaven in 1914. In the year 2014 his 1,000 year reign will be 1/10 over. Not very significant. So, the overlapping generations doctrine is a drum they can beat for decades.
The truth is, millions now living (who are Witnesses) will die. Even worse, look at the number of Witness who are alive now, lived through the whole 1975 debacle, are in their sixties, seventies, or eighties, and are completely unprepared for retirement. I truly believe the reason why such ones keep a death grip on the religion is that it would be too emotionally devistating for them to come to terms with the truth: the wasted their entire life for a lie.
I was born in the seventies. I remember as a child in the eighties be told by people in my congregation telling me I'd never attend high school because this system would end before then. Now, those kids like myself have children graduating from high school.
When I was in my late teens I would paint members of my congregation into a corner. They might complain of something they are dealing with due to their age. They would turn to me and say,"Just wait until you're old." I would reply,"I'm never going to get old." I could see in their face they wanted to say,"Keep telling that to yourself, kid," but wouldn't. They would clinche their teeth and say,"That's right." To do otherwise would imply that they do not believe the end is just right around the corner.