In theory, the lender could sue the debtor in the US, and then have the judgment registered in the country where the debtor resided. As long as the debtor lives in a country where the US has a treaty recognizing US civil laws, the debt could be personally enforced using local laws.
Or the creditor could take the court judgment to any country where the debtor owns property and, assuming a treaty recognizing US laws, could attach the property according to local laws.
BTW, our local Bankruptcy Judge just got back from Ireland & says bankruptcy laws require payments for 13 years and no exemptions. Yikes!
I'm not quite certain if this is a real question. My guess is that they would be unable to get a loan that wasn't secured by some sort of personal property that would make it worthwhile to flee the country with the "cash". Most large loans require you to "secure" it with equity in personal property. But, beyond that, if that was the intention when getting the loan one could argue that the "person" was committing civil and criminal fraud and could be prosecuted for that and for theft by deception. Doesn't sound like a good idea by any accounts.