Super-mod accidentally (not knowing what he was doing) deleted all variables with sub-categories. It takes 1-2 hours to add them back. Can I somehow restore variables?

You could attempt to contact a site staff member, supposedly leaderboard backups do exist (though I wouldn't know personally).

Leaderboard backup do exist

Send a request to support hub explaining that the categories got deleted by accident and you should get a rollback

Also this has happened to me before, a mod deleted all categories by mistake so I requested a rollback and they accepted