Thanks for confirming – I've updated it as I would do it, which is to mark any existing buildings as demolished:building=* and the entire area as brownfield (this can be updated to construction if/when work begins on building a replacement). Note that the demolished buildings don't appear on the render but they're still present as mapped polygons, so any editor will see them and realise the buildings are demolished, so don't need to be remapped.

Regarding the lumps of buildings in the south corner, if they are the remains of actual buildings I'd map them the same as the rest of the buildings are now mapped. But if they're just piles of rubble that have been placed there, there's no real need.