I don’t want to copy/paste my existing thoughts but I’ll reiterate that moderator actions with optional notification are, in my opinion, the best way to go. How this would be implemented in Discourse’s UI is not immediately obvious to me, but this seems the most valid.
A stopgap measure might be showing the deleted post only to the user who made it with the deletion styling. That would require the least effort as far as implementation goes: just show a user’s own deleted topics to that user.
Edit: Screenshot of how XenForo does it:
