Situation: Someone makes a post asking a question. I spend time answering it. Then the post is deleted.
I can no longer access the post and therefore can not find the author to block them.
What I do have is a link to an empty page.
How do I find the author?
What if they edited it first?
The solution seems to me to be a moderator job for someone abusing the system. They should be able to see in the logs things like this, so just need to be notified of when it happened. They could probably look at your post attempt and tie it to a name, then research that name to see if it’s a common activity. Next step is to give the user a warning (again, assume innocence first) and go from there.
Coming from the Reddit mess years ago, if I decide I want to delete my content, I want that ability. For whatever reason. If you want to take their post topic or content and open up your own post using it to continue, you have that ability.
That forces one to spend extra time to restart things that were already started. At the same time, I can see the need to allow people to delete things they might have realized they revealed too much in (or some similar reason).
My suggestion would be involving mods (although I hate to put more work on them) via a process that allows OP to request deletion, then hide it until a mod can decide if it should be deleted entirely, or just the username disassociated from it so the conversation isn’t abruptly yanked from participants.