SixofNine...you don't have kids, do you?
Why? Because I implore you not to treat your child like a mentally challenged person?
Not only do I have a daughter, but she is one of the most well rounded, immune-from-ever-possibly-becoming-a-JW persons I know. When she was six, I had to tell her why daddy wasn't going to the meetings anymore. I did this in spite of the fact that she didn't ask directly; but I knew she must wonder. Six months later she asked if I would be home from work in time, because she didn't feel like going to the meeting with my mom and sister. I made sure I got home in time. I don't think she ever went to another meeting. (I realize your kid won't likely have the same options)
I can't even imagine what good you think you will accomplish by not giving your child a straight answer to his question. I'm sitting here thinking of different scenarios, and they are ALL worse because the kid has this question hanging in his mind.
But you tell me, what message are you trying to send by avoiding the question? Or what message are you trying to avoid sending, and what is the benefit of not sending it?
Think about, you've drilled it into your kids head that people who don't go to meetings are going to be killed at armageddon. And armaggeddon is coming soon. Don't you think you have some responsibility to let him know that you think that is all a bunch of malarkey now?