It does when I think on it in a universal sense -- it's not like I know which way is what. That's sort of Kant's point: Keep on arguing which way you want, it'll be interesting, but it won't effect scientific knowledge and you'll never know which is what.

If Kant thought it worthy addressing philosophically then I have a hard time arguing determinism isn't even plausible in the manner you described.

Cool.

I wonder if someone who doesn't exist at all can question his own existence or non-existence?

I am not, therefore I don't think.

What difference would it make if I had not existed? To me, nothing; to others, a lot.

Any single on of us? Likely not too much. Maybe some people would be less happy - heck maybe they'd be happier, it's difficult to say.

I'd miss out on everything quite literally. But the universe does not care one way or another.