After April 12, 1974, the inclusion by incorporation, consolidation, or annexation of any part of the assigned service area of an electric utility within the boundaries of any municipality shall not in any respect impair or affect the rights of the electric utility to continue and extend electric service at retail throughout any part of its assigned service area unless a municipality which owns and operates an electric utility elects to purchase the facilities and property of the electric utility as provided in section 216B.44.