The lifelong atheist and rationalist Bertrand Russell was once asked this question.

Some human: Lord Russell, what will you say when you die and are brought face to face with your Maker?
Russell: God, why did you make the evidence for your own existence so insufficient?

I’d say this: Hey Dude! Wow. Hehe… you know I was just trying to make those religious fanatics more scientific, right? Wow, I had no idea. Seriously! Very cool. What is this, then? Some parallel universe thing? Fifth dimension type deal? Oh, I see. Just is. Well, thanks. Does that “other place” exist too? It does?
Hehe…. (nervously)… glad I’m talking to you then!
So, the big bang. Was that you? Dark energy? That you too? Dark matter holds the galaxy together. That you too? Higgs boson really the God particle? No? Just an indicator? Cool. Can I go back and tell everybody else? No? Shoot. Well, anyway, glad we finally had this talk!