From: Rabbi Moshe Sofer
To: Unknown recipient
The Chasam Sofer rules that the custodian of a promissory note belonging to an apostate who died leaving Jewish heirs would commit a transgression by producing the note and handing it over to those heirs. Since the apostate's lien is considered extinguished upon conversion, the custodian need not inform the heirs of the note's existence; at most, he may compensate them for the negligible value of the physical paper itself.
Source: Shu"t Chasam Sofer CM §154