I know this is a bit of a speculative question but about how long would any evidence of a pre-industrialized society last? Had mankind died out from the Black Death how long would there have been evidence that humankind had even been on the planet?
Given that we have evidence of humans (Homo erectus) using fire from 1 million years ago, and that is far from the oldest evidence of hominin activity on the planet, I would say that it would last for a very, very long time. I was just on an excavation this summer that demonstrated evidence for human occupation at the site of Ashkelon from around 3000 BC (Chalcolithic-EB1 transition).
There is no doubt that evidence of human occupation can stick around (and does stick around) for millions of years. An exact number would be difficult, but would be quite high.