Completely Locked out of website via User Permissions
It sounds like the roles database table got randomly deleted, which should basically never happen under the circumstances you describe.

If you have a recent database backup, I suggest you grab the structure and content of the roles table from that database backup and restore that to your site database so you have the right content.

If you don't have a backup, I suggest you do a new installation on a separate site (or your local computer) and then export JUST the roles table from that new installation and import the roles.