* The Ruins of Earth: An Anthology of Stories of the Immediate Future, 1971
Thomas Michael Disch (February 2, 1940 – c. July 4, 2008)
The human race is gone, forever! About bloody time.
What survives depends on how you want them to have gone, suddenly and mysteriously (which becomes a plot point) or violently and with maximum collateral damage. Whichever way you choose will determine the state of the physical environment. Remember however that most human structures built these days are not designed to last much more than 100 years, concrete and steel corrode and buildings collapse, nature re-asserts itself very quickly. Either way the remains of humanity will provide rich resource fields for foraging Mechs.