If the Apportionment Commission fails so to certify such establishment and apportionment to the Secretary of State on or before the date fixed or if prior thereto it determines that it will be unable so to do, it shall so certify to the Chief Justice of the Supreme Court of New Jersey and he shall appoint an eleventh member of the Commission. The Commission so constituted, by a majority of the whole number of its members, shall, within one month after the appointment of such eleventh member, certify to the Secretary of State the establishment of Senate and Assembly districts and the apportionment of senators and members of the General Assembly.