It wasn't a moment in my life when I came to the conclusion that the Judeo-Christian God doesn't exist, but rather a slow realization that there simply isn't any objective evidence to support it. The historical and scientific record don't support the story and there are huge logical problems in the Bible, specifically about God's actions and the role of Jesus. I just came to the conclusion that the Bible is just another creation myth and is no more real than the Greek myths about Zeus or the Norse myths about Odin.
I won't rule out the existence of some supernatural force, but if it does exist, I suspect it is something akin to the Deist conceptualization of God, as a prime mover who starts the universe and then promptly does nothing with it. Or something like the Force is which everything is interconnected. Or maybe something no human can even wrap his brain around. However, I don't think that version of a god is a personality like Jehovah. Again, I have no data either way for the existence of the supernatural.
As far as death, who knows. I suspect that as I lose consciousness and my brain dies it's like falling asleep. I just fade out and that's that. However, I may be entirely wrong. If something akin to the Force does exist and we're all interconnected on some level, then I guess I would join with that. I just have no belief in the Judeo-Christian-Islamic version of heaven or reincarnation or going to Valhalla.
My belief system comes down to three tenents:
1) You get one shot at live, so make the most of it. Live, learn, love.
2) Don't be a dick.
3) Aspire to be more than you are. Don't settle and don't stop.