> Well at least the database can be queried easily for usage of that
> tablespace.
Yes, that's the easy part to fix. You'd just set the dattablespace back
to 0 when you dropped the tablespace.
> For the namespace issue, it would help if *some* object would be created
> with that namespace (e.g. an empty directory or file with the namespace
> oid), so that pg_tablespace_databases() could detect it.
Seems like the only way.
Chris