I would suggest that an Atheist will either make the claim that they don't exist which is ridiculous because how can an atheist that doesn't exist claim any stance at all?
Or secondly, an atheist will adopt the stance that they do exist but not in a way that the human experience matters ultimately.
I would suggest that if you want to bring the human experience into the debate then you need to make a clear distinction between "exist" and "alive".
I would suggest that you need to divide atheists into two camps therefore.
Those that believe that they don't "exist" which is a puzzling stance as I have explained above and those that believe that they do "exist" but don't believe that they are "alive" but rather believe that they are "dead".