So, I haven't read the whole thread because it's goddamn enormous, but, here are my views on the matter...
First of all, obviously as many have stated, there's no way anyone can know for sure. That's elementary.
But more importantly, I don't know if anyone has mentioned or suggested this yet, but I believe that we live in a world that is not only completely incomprehensible, but simply has realities that are paradoxical by any and all means of rational thought.
Take existence in and of itself, for example. It would make perfect sense to me if nothing existed at all, anywhere. An eternal vastness of empty space; that, to me, is perfectly comprehensible. But things DO exist, and logic dictates that every effect must have a cause. So right there I see an inexplicable conundrum already. I think at this point it all comes down to two distinct possibilities: Either things in the universe have simply always existed, or there was a time when nothing existed, and then things somehow came into existence. I don't think either of these two scenarios can be explained or understood by any kind of human logic or rationality; therefore, whatever the truth is, it completely defies anything that we consider to be "possible."
I use this line of thinking to explain some of my views on other different kinds of things in life, be they philosophical, ethical, or what have you. The point is, the idea of something like a God creating the universe is completely ridiculous, but no more ridiculous than the idea of the Universe having come into existence without one. That's my view, anyway, and as such, if it's possible, so to speak, that God exists and he created the Universe, then it's also possible that there's an afterlife to which we all go. I have a lot of ideas on the nature of God and the world, but I won't get into that here.
Having said all that (and now to diminish my credibility, hahaha...) I have always believed in God and the afterlife, and I fully acknowledge and accept the fact that my only real basis for that belief is that I need it to be true to maintain my sanity. I also realize that this is obviously an extremely weak foundation for believing in something. But that's just the way it is : D
Edit: When I think back on it, I think I first started becoming truly suicidal when my brother made a whole bunch of extremely compelling arguments to me that God and the afterlife don't exist, and I believed him. He turned my head completely upside down, and a once disturbed human being (myself) was made all the more worse for the wear. I'm not blaming him or anything. I just can't cope with it. Even as a child I occasionally had panic attacks at the thought of God and heaven not existing, and just fading into oblivion. I have always had an irrational fear of not existing.