The structures of the Amaurotines were impossibly durable, so it is likely they still exist somewhere on the Source, but just buried deep beneath the earth or at the bottom of the ocean or in some other extremely inaccessible location. Even after 10,000 years, the structures on the First showed not even the slightest blemish or crack, they were just half-buried and covered with debris and overgrowth. The only damage they ever sustained was from the Final Days catastrophe. While I don't think any of the visible areas we've seen so far on the Source are from that time, I suspect we will be seeing something in the future as we delve further into the true history of the planet.