If such Apportionment Commission fails so to certify the establishment of Assembly districts 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. Such Commission, 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 Assembly districts.