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.
The building problem might actually be less of a problem long term, as Lusatia is experiencing population decline. One of the towns mentioned Hoyerswerda went from 71k in 1981 to 31k today. So giving up some buildings is probably going to happen anyway. Might as well go for the ones with ground water problems.
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.