If my wife didn't exist, that would make a huge difference in my life for the worse. Same goes if my daughter, her husband, and my granddaughter didn't exist. I'd feel the loss terribly.
But when it comes to God, so what?
God has had absolutely zero influence on me during my 73 years of living. I've never had any sort of relationship with God.
The only effect God has ever had on me came from my attitude toward God, my belief or lack thereof in God, my imaginings about God.
So if God exists, or if God doesn't exist, that makes no difference to me. Or I'd say, to anyone else, for we all create God in our image, or non-image.
There's no evidence that God has ever had any effect on anybody. All we can say is that believing in God, or not believing in God, has effects on people.
This is much different from, say, gravity. Gravity, unlike God, clearly is real. I drop something and it falls to the floor. That's gravity at work.
If gravity didn't exist, that newfound lack would change life on Earth so dramatically, life wouldn't even be possible anymore.
With God, though, believers and unbelievers in God live their lives in the same way, because God has no evident causal influence on anything or anyone.
If you disagree, share in a comment exactly how you know God makes a difference in your life.
What would be different if God didn't exist? To atheists like me, that's a trick question, since we're virtually 100% certain that God is a fantasy, so God already doesn't exist in the lives of believers.
Again, only their belief in God exists, not God.
As noted in a recent blog post, Philip K. Dick said, "Reality is that which, when you stop believing in it, doesn't go away."
When people stop believing in God, God goes away. This shows that God isn't real. By contrast, stop believing in gravity. You'll find that gravity is unaffected by belief.