The Saudi royal family can make a profit at $10/barrel for a few years, then they lose control of the country and the oil because they had to stop most of the bribes (social services, etc) they were paying the population to continue to go along with the regime. (The Russian government is in a similar situation to some extent.) But yeah, someone in Saudi will continue to sell the oil, maybe after a few months or a few years of chaos, even if they can only get $10/barrel.