The way this works, is that we have a profile called 'deleted' and everything a person has contributed is reassigned to that profile. Then we really do delete the profile of the user in question.
We do warn, in advance, that once done the author loses all right to their content forever. As we could never know who the author is. But then... this shouldn't affect HN as you already lose the ability to edit your content after some short amount of time... the effect is much the same as permanently losing ownership of your content.
The 'deleted' account is the accumulation of all content created by profiles now deleted. Here's the deleted account on one of my larger forums: https://www.lfgss.com/profiles/47687/
This method of profile deletion means that none of the conversations that have occurred lose their meaning, or are otherwise broken up or left 'gappy'.
BTW, I've always found it a bit strange that HN doesn't seem to have legal documents, user agreement or privacy policy.