The purpose of legal heirship certificate is used to establish the relationship of the heirs to the deceased for claims relating to pension, provident fund, gratuity or other service benefits of central and state government departments, specifically when the deceased has not selected a nominee.
Banks and private companies also accept such certificates for allowing transfer of deposits, balances, investments, shares, etc. If you are for some reason not able to get the legal heirship certificate then you can go a succession certificate.
The Indian Succession Act, 1925 defines a succession certificate as a certificate issued by a court to the legal heirs of a deceased to establish the authenticity of the heirs and give them the authority to inherit debts, securities and other assets of the deceased. However, out of the two succession certificate is difficult to obtain as it requires death certificate.
You can use any nomination that your father would have filed with the office. A person is only considered dead if he has been missing and not heard of from anyone for a period of seven years as per Section. 108 of the Indian Evidence Act. So, you cannot procure a death certificate too. These are the only available substitutes to legal heirship certificate.
Reference: Indian Succession Act, 1925, Hindu Succession Act, 1956