I didn't even go to Catholic school, but in the process of Confirmation I learned enough apologetics to deflect or reject or just willfully not understand most of these.

A Good Catholic will tell you that the universe could not exist without God, and/or that nothing good can exist without God, so if there were no God, there would either be no universe, or the universe would be hell.

It would sort of be like me trying to convince you quantum physics is wrong and starting out by saying, "Imagine a world without quantum physics." You have nothing with which to substitute quantum physics. Your mind returns a divide by zero error.

Additionally, religious folks in general tend to claim to believe that morality comes from God. And when they say this, they really truly mean that if there were no God, there would be no morality. That the fact that morality exists is a kind of proof that God exists. I am not making this up. I have been told by a religious person that, if they were to learn that God did not exist, they would immediately embark upon an orgy of murder and theft, because, "There would be no reason not to." They believe this about themselves despite the fact that we know it to be a misunderstanding of psychology. I am not saying all religious people have exactly this glitch, but I am trying to emphasize that your friend(s) probably don't have the cognitive algorithms in place to even comprehend these questions the way you mean them.