Would I exist if my parents had never met...?

No. If your mother and father had never met, and if one of them had mated with someone else, their resulting offspring would not have been "YOU". "YOU" would never have existed and would never have been born at all. The unique "YOU" is a combination of your mother and father's genes and DNA, and that of your grandparents and great-grandparents - all the way back on your family tree.

No two human beings on the face of this earth share the same genetic make up and DNA, with the exception of identical twins. Your blood brothers and sisters share some of the same genetic components as you do because you all have the same mother and father, but they are not exactly the same as "YOU". YOU are a unique human being, and there's not another one exactly like you on the face of this earth.

Oh why oh why did your parents ever meet? Because my life would not be complete without saying NO five hundred times a week.

No - Simply putting it, you were or are your mum's egg that grew inside her body so your genes were only in that one egg and once fertilised (touched by the sperm,) it started to make you!

No. This question does not arise in that case.

No. Because biology.

You would still be your father's sperm.....

No

No

probably not

no