If it’s a member that has no posts, it would be like 10 (or so) core tables (members related, follow, reputations, ignore, etc). If it is a member with many posts, and I’m not talking about topic post, it’s more like any content type, all I said plus dozens of tables (content items, comments, reviews, other tables that stores member ID)… not to mention plugins that stores data.
Believe. Better to restore a backup.