It should be "you will lose more than that when the king gets through with you" - there is an 's' on gets. "Gets through with" means 'finishes with' - i.e. finishes doing whatever he is going to do. It means that whatever you have already lost, you will loose a lot more, when the king finishes (probably punishing) you. In the old days, kings had the power to remove quite a lot from you - your land, your money, your head...