@Ricardo Rodriguez: as far as OSM is considered, we only map what is still there. So we map ruins, but as soon as the last stone disappeared, you have to use the OpenHistorialMap that SomeoneElse mentioned.

The only exception to this rules seems to be railways, as one can still see cutlines or embankments when all the rails are removed.
Although I prefer to map the embankments and cutlines, rather than the demolished railway.