@Kirin-kun
Well, there's a bit of magic involved, but there's a ton of people that were completely broken.
Here's some of the destruction to the cities we see in chapter 1:
You can see a lot of people getting destroyed.
Here's more of that also from chapter 1:
There's bits and pieces of "statues" everywhere...
Also, a lot of the survivors were below ground, they got preserved because dirt covered them, ultimately protecting them from destruction, as seen here with Taiju from chapter 14:
So yeah, a lot of people are dead forever because of accidents during petrification and then because of the weather, natural disasters and time.
Traces of our civilisation would be destroyed, buried or decomposed. Maybe if they start digging, they would find things like concrete or some metal that wouldn't have completely rusted away, but that wouldn't really be a good use of their time.