When you assign a persistent identifier to your Koha record (auth or biblio) and you delete that record at some point in time, it would be good to resolve the persistent identifier to a gravestone/tombstone page that at least tells that the record has been deleted, perhaps even more.
See also bug 30888, that proposes to add a deletedauthorities table.
It's an interesting idea. I first bumped into it using Fedora 4.x where they have a similar tombstone concept: https://wiki.lyrasis.org/pages/viewpage.action?pageId=34649759 Maybe we could have a system preference to show a tombstone page if there is an entry in the deletedbiblio table and we could return a status of "410 Gone". That seems like a pretty straightforward solution to me. I think having a system preference is probably a good idea as people might rely on the current behaviour... which actually redirects to 404.pl with a status of 200. Huh. That's not so great either...
Bug 30888 provides a foundation for the authority side now by keeping the deletes in a table.