Borrower absconding after taking money

My father lent a part of his retirement maturity amount to his friend who promised us with monthly interest payment and full principle payment after some 2-3 years and they have made a agreement on it. The borrower paid the interest for few months and suddenly absconded by leaving a note that he can't pay the amount as he has suffered losses in his business and he ran out of money to paying back. we filed a case against him and civil , missing case is registered on him. when we asked their parents to repay the debt , they told us that they are not responsible for their son's debts. But, we knew that the borrower's father has lot of immovable assets like agriculture lands and house on his name . It has been 3 years and still we are not able to find a solution to this. This affected us financially and emotionally very bad as the amount is my father's retirement amount with which our whole family is dependent on.