> One time, me, a noob, accidentally deleted files in the PG data directory. No noe! But PG had open handles to them so they aren't reclaimed by the FS and I was able to pg_dump. Not a production system but the loss would've been "big". Just saying, PG itself is very resilient.

That isn't a PG thing; Linux[1] ext3/4 does not actually delete files (or directories) that are still in use. Only the name is removed. The file itself remains until the last open handle to it is closed.

[1] Amongst other OSes