Zen is the art of being totally immersed in the moment. This second, this breath is all we have. Everything else is illusion. In Zen we attempt to strip away all the fluff, all the unnecessary wrappings that hold us back from full awakening. So what many will call my overly simplistic response is: "We don't worry about things like that." If you knew for a matter of fact, with every cell of your body that God did not exist, would you change the way you live? So far everyone I have asked have said no. Then? The Buddha taught that all sentient beings have everything they need within them. When we seek externally, we hold ourselves back.
Developing compassion to the point where all our thoughts, deeds, actions, our very essence are ruled by compassion and wisdom is the utmost expression of our buddha nature. So I would say if someone's answer to the question above was "Yes," they have more work for the cushion, and that it is more important than the other existential questions we can become bogged down with.