Lets say that tomorow it will be proven that God doesn't exist , religion will fade ,

[Whateverist]

You can't prove no god any easier than you can god so long as 'god' remains undefined.  Next question.

I see the problem " Does God exist?" irelevant, because it doesn't affect us.

God's existential status doesn't matter to me either, but it certainly does affect a good portion of the population in the U.S., especially the enormous chunk that subscribes to a fundamentalism.

But the point of what I wrote was to say that the premise in this thread's title is faulty because disproof like proof of the undefined is not possible. So speculation about a tomorrow that follows upon the impossible is pointless.