PLEASE get full details of documents signed by the borrower for appropriate opinion
CHECK for any document other than the promissory note
However, based on promissory note alone the lender can at best file a money suit , generally ( even in banks also ) the promissory note does not bind legal heirs of borrower
If the borrower had signed only promissory note then if will not be possible to recover from the legal heirs
BUT, if the borrower had some left properties then the lender has recourse of recovery from the holders of that property