On Account Deletion, also Delete Associated Chats
My instance also got hit by the massive account creation/spamming operation
My instance is configured to send a DM to new accounts, configured via Admin FE. That welcome message process creates a chat record for each new account.
During the process of manually deleting the many spam accounts, I also had to manually leave each chat that was auto-created by the welcome message function
I think it would make sense to remove associated chat records when an account is deleted