In eastern Germany, enormous pits carved into the landscape by decades of lignite mining are being transformed into a vast network of lakes, wetlands and restored land. The Lusatian Lakeland, spread across Brandenburg and Saxony between Berlin and Dresden, is being created by flooding former open-cast mines and reshaping their surroundings.
Even for empty buildings this can be a problem. Because nobody takes care of them the city will need to take care of it to prevent the Building to negatively impact adjacent Buildings (e.g. structural hazard due to instability).
And if it affects public buildings (schools, City Council, etc.) they are directly affected. So yeah… quite messy.
The buildings are usually demolished. Google Maps has some issues in that area, because roads have been removed, as they would only lead to demolished commie blocks. Housing is super cheap though.