The merger shall become effective upon the last to occur of the following:
a. In the case of a mutual depository, on the date the approved merger agreement or plan of acquisition is filed with the department as provided in section 10 of this act;
b. In the case of a capital stock depository, on the date the stockholders' vote is certified to the commissioner as provided in section 11 of this act; or
c. Where required, all necessary federal approvals have been obtained or waived.