500. Where a school board withdraws from a regional school board contemplated in section 362, the secretary general of the regional school board shall, where necessary, within 30 days of the coming into force of the order, provide for the election of every commissioner representing the parents of the minority of students contemplated in section 146 in accordance with the procedure prescribed in the said section. The person elected shall remain in office until he is replaced by a person elected pursuant to the said section.