All perfect praise be to Allah, the Lord of the Worlds, and may His blessings and peace be upon our Prophet Muhammad and upon all of his family and companions.
Dealing with usurious loans is forbidden in all forms, since Allah, said(what means):" O ye who believe! Fear God, and give up what remains of your demand for usury, if ye are indeed believers." [Al-Baqara/278]. Therefore, whoever has taken a usurious loan must pay it off along with making repentance and seeking forgiveness.
The heirs are not obliged to defray their dead father's debt since the insurance company has already done so; therefore, your father is free from the liability before Allah.
In addition, if some of the heirs wanted to absolve their father from that sin (dealing with Riba), we advise them to give charity on his behalf along with making supplication to Allah since good deeds annul misdeeds. The Prophet(PBUH) said (what means):" When a man dies, his deeds come to an end, except for three: A continuous charity, knowledge by which people derive benefit, pious son who prays for him." Sound Hadith [Al-Trmithi]. And Allah knows best.