Upon the liquidation of a domestic reciprocal insurer, its assets remaining after the discharge of its indebtedness and policy obligations, the return of any contributions of the attorney or other persons to its surplus, and the return of any unused premiums, savings or credits then standing on subscribers’ accounts shall be distributed to its subscribers who were such within the twelve (12) months prior to the last termination of its certificate of authority, according to such reasonable formula as the superintendent may approve.