What is the ruling of Sharia on this incident, and what is the right of my mother?

The blood money (diyah) is incumbent upon the 'aqilah (male relatives on the father's side) of the fleeing perpetrator, if the incident occurred due to error. This is based on the Almighty's saying: "And it is not for a believer to kill a believer except by mistake. And whoever kills a believer by mistake – then freeing a believing slave and a compensation presented to his family [is to be made], unless they [his family] remit it as charity." He has no right against the employer except what is stipulated in his employment contract. As for the commercial insurance company, it is obligated to pay all the premiums that the deceased paid to his heirs. If your father had a right against the employer or insurance premiums, then you have the right to claim them from both, and if they refuse, you can complain about them to the relevant authorities.