The mere potential for any life to exist, from the most basic single celled organism to the most complex sentient, necessarily precedes any manifest physical existence and survives postmortem. As Stephen Hawking put it so well, information cannot be destroyed.

On that basis alone I would have to reject existentialism and it's mantra of 'existence precedes essence'. That potential is most certainly a characteristic of essence. Furthermore I do not believe any argument can demonstrate that such potential does not precede existence. Any such argument would have to demonstrate that potential did not exist prior to the big bang, which is when physical existence as we know it came into being.