The policies shall provide for a premium or premium deposit payable in cash and, except as provided in this section, for a contingent premium at least equal to the premium or premium deposit. Such mutual company may issue a policy without a contingent premium while it has a surplus equal to the capital required of a domestic stock insurance company transacting the same kinds of insurance, and in no event shall the holder of any such policy be liable for a greater amount than the premium or premium deposit expressed in the policy. If at any time the admitted assets are less than the reserve and other liabilities, the company shall immediately collect upon policies with a contingent premium a sufficient proportionate part thereof to restore such assets, but no member shall be liable for any part of such contingent premium in excess of the amount demanded within one year after the termination of the policy. The commissioner may, by written order, direct that proceedings to restore such assets be deferred during the time fixed in such order.