That doesn't stop it being necessary in a debate scenario. If you can't prove your claim, don't make the claim. It may very well be the case than during a debate, someone says 'but God doesn't even exist' without anyone specifically claiming that He does. In this scenario it is not up to everyone else to prove the guy wrong; he's the only one who actually made a claim about God, so he's the only one who has to prove anything. As far as the other guys are concerned they were just expressing opinions rather than intended truths. If you can't prove 'God doesn't exist' then don't claim it in a debate scenario. Simple as. If you have to say something then state your opinion because you don't need to prove your opinion.

Nobody should claim that God doesn't exist. That would be a stupid assumption. God cannot be disproven so don't claim that try to claim that he doesn't exist. What you should do is look for evidence of his existence. If no evidence exists then you should dismiss the claim that a God exists because it would be irrelevant to talk about it without evidence.