Or, going by history, they'd just be explained away by religion. Given that all the easy-to-reach, high power density fuel sources have been depleted, it's not unreasonable to think the next civilisation may be stuck in the preindustrial era.

Also, geosynchronous orbits are only stable on short-ish time scales (tens to hundreds of years). When talking about tens of thousands or millions of years, you've got the perturbing forces of the Moon, the Sun, and the ellipsoid shape of the Earth all adding up. I'd be surprised if any of them are still up there by then.