The witches of Discworld are not exactly known for selling themselves to anything. If organising atheists has been likened to herding cats, getting witches to do anything they weren't going to do anyway would probably be like trying to eat Mount Everest, using New York skyscrapers for chopsticks. Granny Weatherwax, for example, would probably make your Yazkinoth wish it'd never been born; while Nanny Ogg would probably make fun of its genitals in some earthy pub folk singing.
At the age of five, Skagra decided emphatically that God did not exist. This revelation tends to make most people in the universe who have it react in one of two ways - with relief or with despair. Only Skagra responded to it by thinking, 'Wait a second. That means there's a situation vacant.'
