The board of [the] merging district shall notify the board of the merger district of the results of the election. If three-fifths of the votes cast at the election favor the merger, the respective district boards shall adopt concurrent resolutions, declaring the districts merged, under the name of the merger district. Thereupon the districts are merged into one district, under the name of the merger district; the merging district is dissolved without further proceedings; and the boundaries of the merger district are thereby extended to include all the area of the merging district. Thereafter the legal existence cannot be questioned by any person by reason of any defect in the proceedings had for the merger.