Dancing Gods — Jack L. Chalker

BEYOND THE SEA OF DREAMS
Life had never been kind to Joe and Marge. Now, according to Throckmorton P. Ruddygore--a stranger who met them on a road that wasn't there--they were due to die in nineteen minutes. But across the Sea of Dreams lay a new and perhaps better life, in a place where fairies danced by moonlight. Joe could become a mighty-thewed barbarian warrior. Marge could be beautiful and find her magical self.
It was just as Ruddygore had promised, plus a great deal more. For this was a world where Hell still strove to win its ancient war, where demon princes sent men into battles of dark magic, and where Joe and Marge must somehow help prevent the coming of Armageddon!