See that's the thing- through inductive reasoning, not deductive reasoning, there is NEVER a 100% proof, but rather 99.9%
Take gravity, for example. We know what it is via inductive reasoning- thus we are not, and CAN NOT, be 100% certain that gravity exists. But we are 99.9%, know what I mean? Anyone would bet their life that if they dropped a pencil, it would fall. Anyone would bet their life on the law of gravity, even though it was reasoned inductively.
That's how we would 'prove' the inexistence of god- through inductive reasoning, not deductive. Therefore, it won't be a 100% proof. The question is, would you face the truth if it were 99% correct? Most atheists probably believe it's at least 95% or higher, if I were to hazard a rough guesstimate