If any provision of this 1977 amendatory act, or its application to any person or circumstance is held invalid, the remainder of the act, or the application of the provision to other persons or circumstances is not affected. In the event the provisions in RCW 36.56.040 requiring approval by both the voters of a central city and the county voters residing outside of the central city are held to be invalid, then such provisions shall be severable and the ballot proposition on the transfer of the metropolitan municipal corporation to the county shall be decided by the majority vote of the voters voting thereon in a countywide election.