W H A T ..... I F ..... mmmm .... there were no Gods !!
Let's say, science one day proved to complete certainty beyond any doubt that there are no Gods .. none.
What would this world look like?
More or less chaos ? The same, certain types of conflicts would stop, certain types would surge.
More or less wars ? Less
10 commandments ? Well, a lot of non religious people try to do good things for their peers and the people around them. The 10 commandments would still be a nice way to be nice to others hoping they'd be nice to you in return.
Purposeful or meaningless life ? That's up to each person. The meaning of meaning might change but you might still find a motivation to make something happen in your lifetime, especially since it would be all you get.
Reasons to live or die? No change.
Reasons to construct or destruct ? No change. Idiots will be idiots, Valuable people will be valuable.
What does it all mean ? What means what?
What would change ? Not much. One of the eternal debates might end. Some manipulation would stop.