Basically, if he plans to keep working, he will pay the money back eventually. If the loan iwas secured using a federal guarantee program, it won't be discharged without showing undue hardship (i.e., total disability). They will refer the loan to collections, take his income tax return every year and garnish his bank account and wages (up to a certain amount, e.g., 15% of disposable income). This is an administrative process. It is done by notice that a decision was made to start the garnishment on a particular date. The borrower has limited grounds to appeal. I suppose he could try to negotiate for rehabilitation at that point, but I am not sure.
It might take a year or two before the garnishment occurs, but until that time the interest keeps accruing on the principal. So, the real issue is how long can he hide.