They could still find stone in less monumental form. There are identifiable stone tool workings that are more than two million years old. Mind you, flint is fairly hard stone. Marble statues would erode if left exposed, but could be preserved for quite a long time under the right conditions. For that matter, good concrete can last a very long time. Maybe not 10,000 years, but we really can't be sure, since we haven't actually left concrete out for 10,000 years yet. Estimated time for various plastics to decompose varies widely between types. Some may outlast 10,000 years by quite a bit, although it might become unrecognizable to casual examination much sooner. Glass can last a very long time; glass relics are the modern equivalent of historical stone as a commonly-used but highly-durable material. After 10,000 years, there might be little of man left on the surface, but study in more depth and it will take far longer not to turn up clear signs that somebody was here and making a mess.