Accepting one's mortality is a natural occurrence, that takes place as one gets older. Unfortunately, JWs are generally very stunted in this area of growth, among others. When one learns that they are not going to cheat death, especially too late in life, I would imagine it would be very disconcerting.
There are all kinds of problems believing one is going to live forever causes along the way though. Not planning properly in terms of education, career, retirement, etc., for one. Becoming insensitive to other people's problems, health, and ultimately death, for another. Missed opportunities all around because of waiting for "the future life", yet another, ad infinitum. I did fine on the education, career, and hopefully retirement parts, and making up for the lost opportunities all the time, but the insensitivity I cannot take back. I can only improve on that moving forward.
I don't think I personally ever really wanted to live forever in that Stepford world. I think this helped to allow me to focus on what I can do now, even while I was still in. It is just multiplied by at least 1000 now. And while I am not ready to die just yet, I have come to accept a long time ago that I will die someday.
d4g