I’m not sure I understand the question. M’dinei Shamayim, you should repay money you owe, even if it can’t be collected in court or by a Beis Din.
If the lender/vendor wants to take you to Beis Din, the Beis Din will figure out whether or not at the time the debt was incurred, you intended to make the debt dependent on American law, which you would have been entitled to do.