When any person elected to a public office has died or failed to qualify and enter upon the duties of such office for any reason or cause at the time and in the manner provided by law, and for six (6) months or more thereafter has not qualified and entered upon the duties of said office, such public office shall be deemed vacant and shall be filled by the officer or board authorized to fill such vacancy, provided, however, that any appointment made under the provisions of this section to fill an office of any person who has failed to qualify on account of military service shall be only for the period of enforced absence of said person, or until said person qualifies for said office. The person holding over in such office shall surrender the same to the person so appointed upon his qualifying for said office as provided by law. The provisions of this act¹ shall be retroactive as well as prospective in its operation.