I think the reason some JWs are "ok" with the end not coming in their lifetime is because they werent signed on for the reward of the paradise to begin with.
Some are idealists who relish the thought of being part of something big and "right". Something that aligns them with God in an intimate way.
They (in their minds and hearts) are floating above that whole reward system so it doesnt make it a deal breaker.
It will come eventually (their belief) and in the meantime they are showing God and the world that they stand for what is right and pure.
There are many "causes" one can adopt. This one is theirs.