One night in July, 2135, there were some eight billion people on Earth. The next morning there were perhaps 400. There was no clue to what had happened to the world's population -- but, over the centuries that followed, still stranger things occurred.
The human lifespan now stretched to millenia instead of decades, and much of the remaining population developed the ability to move at will among the stars -- and abandoned their homeworld for a life in deep space.
Then, after 3000 years, a star-rover discovered what had happened to Earth's original inhabitants -- and that they were coming to reclaim their heritage. Those who had stayed behind knew, with a growing fear, that the mystery of what had been done to Earth and why it was about to be solved ... in a way that would change humanity forever.
Not one of Simak's greatest, although a grand conception. Possibly I didn't like it as much because of the 60's/70's noble Indian, one with the land overview. If you're a tree-hugger, this is the book for you.
A Choice of Gods is a "What the hell happened to everyone?" story, where a handful of survivors wander a mysteriously depopulated Earth.
The disappearance of most of mankind occurred in the year 2135. After an introductory chapter, however, Simak quickly advances us five thousand years, to show us what has become of the sparse remnants of humanity. These folks have enjoyed some nice perquisites from being left behind. For one thing, their life spans have inexplicably lengthened to near immortality. For another, all of the robots people had built by 2135 remain here, so there are plenty of robot servants happy to take care of all the holdovers' needs if they wish it. Finally, people have developed surprising new abilities, including being able to communicate telepathically and to teleport themselves to other planets.