A Choice of Gods

One day most of humankind disappeared. A few human beings were left on the deserted earth along with countless robots. The human beings–including a small tribe of American Indians–made do. The Indians returned to ancient tribal ways, the others stubbornly tried to rebuild technology. The robots–some stayed with the humans performing their service functions, some went off to create a religiously-based society of their own.
Millennia later, a star-traveler returns from the center of the universe. The people of earth had been found and were planning to return. But something else had been found, too–the central intelligence of the universe!