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!