The file is still available online and this is not a mistake like a misslick, this is a deliberate action. He refused to listen to me when I warned him.
Get that in writing. At some point there might be an investigation however small even if just internal, and any email is better than he-said-she-said scenario.
Your CIO is so ... looking for a polite word ... stupid that he must be fired. No doubt. So write an email to him that what he did is too dangerous and must be undone (DB removed). If the databised is not removed quickly, report it. It is your duty.