Steel and concrete might not be in the form of buildings after 500 years, but they'd still be there.
It wouldn’t completely disappear but our concrete wouldn’t do as well as you think. Until very recently, it was markedly inferior to Roman concrete.
My parents worked 5 years in Abu Dhabi. The Arabs were tearing down high rises that were only 30 years old. In their rush to build the high rises, they didn't bother to use desalinated water. Both the concrete was severely compromised and the structural steel and especially the rebar was rusting.
Even taller high rises were built in their place, this time using desalinated water.
