Agreed, quitting is not an easy thing. Whether it is gambling or something else. The owner shouldn't have given money, just because he gave money the victim continued spending. If not, he could've left with what he had lost from his pocket. The trouble maker is the casino owner who knows well about the reality of gambling that it is not easy to recover the losses.
Even if quitting is difficult, they should still try. It would be better for them than taking a big risk that they couldn't take. Both of them have made a mistake and had a problem, which should be resolved amicably. Between the person who borrowed and the person who lent the money, they can discuss how the borrower can return the money. And the lender should be able to provide enough time for the borrower to return the money. The person who borrowed it could return the money by returning it little by little.