I used to think (when having doubts): "Oh well, if this turns out to be false, at least this religion has an expiration date." This was before the 1995 change of doctrine about the 1914 generation, though. Had that doctrine been standing, there would only be ten or so more years left before it would become too ridiculous. Which is why they changed it - in a "foot note" no less. And now recently they also changed the doctrine on all the anointed having been selected already, to now being an ongoing process. Which is also a subtle way of prolonging the 'expiration date' of the religion.
I think they'll be able to continue doing this almost indefinitely. After all, most JWs are still there after these recent changes. The previous teachings are now 'old light'; Jehovah has given them new pieces in the puzzle and the old ones are to be discarded. Just like that. Their kids won't even know what they used to teach on this, I'm sure, and neither will new members. Just as old literature is hard to come by and shouldn't be looked into as it contains 'old light', pre-1996 literature may someday be really hard to come by for an active JW. "Don't dwell on the past, always look forward".
The few who start to think, are literally afraid of doing anything about it. Both because of their friends and family are in, but also because they do believe in Jehovah, and fear him. Well - we've all been there, so no point in me babbling on.