It sounds like “gigantic steel, concrete, plastic and glass structures aren’t just going to dissolve” really depends on timescale, and geologic timescales are far beyond our typical experience.
From the Atlantic article by one of the authors: [1] [2]
When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old—older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. Go back much further than the Quaternary, and everything has been turned over and crushed to dust.
From the Atlantic article by one of the authors: [1] [2]
When it comes to direct evidence of an industrial civilization—things like cities, factories, and roads—the geologic record doesn’t go back past what’s called the Quaternary period 2.6 million years ago. For example, the oldest large-scale stretch of ancient surface lies in the Negev Desert. It’s “just” 1.8 million years old—older surfaces are mostly visible in cross section via something like a cliff face or rock cuts. Go back much further than the Quaternary, and everything has been turned over and crushed to dust.
[1]: https://www.theatlantic.com/science/archive/2018/04/are-we-e...
[2]: https://news.ycombinator.com/item?id=24601382