I read this SF of maybe Fantasy story many decades ago. It was in a collection and the "taste" is Asimovian but he wrote so many stories, so many collections...
Two extremely powerful creatures (aethereal = Fantasy ? or just aliens = SF) make a bet : to make a huge change with a very small intervention. The huge change is to prevent a nuclear holocaust on Earth.
I forgot what the very small intervention was, but it works.
But then, they realise that some supervisor will probably be very angry at them for the change they have caused. So they revert their intervention back to the initial situation.....
