Edit: and what do you know, 16 minutes after cross-posting this to !piefed_meta@piefed.social, Rimu agrees, changes the code, and deploys onto piefed.social to retain deleted posts. PieFed really is something!! (announcement post)
I think they made deleted posts visible in Lemmy 1.0.
I've just done it in PieFed 1.4.3, released now.