Update: I went into the OG database tables, 'og_users', and noticed the user account that I had previously deleted was still in the database. Explains why I was still able to use that account to log in. Doesn't explain why after deleting from GUI, account still exists in database.
I deleted the user account from the database, deleted other records for that user in other tables, went back into the GUI and was finally able to delete the user's personal workspace.