On November 7, 1975, mayor William Hawrelak died in office. After nine ballots, Council chose Cavanagh over Laurence Decore to serve out his term, but when ran to retain the position in the 1977 election, he finished third, nearly ten thousand votes behind victor Cec Purves and under a thousand behind Decore (he did finish well ahead of former mayor Ivor Dent, however). He stayed out of politics for six years following this defeat, serving as chair of the Government of Alberta's Alberta Rent Decontrol Appeal Board (tasked with the elimination of provincial rent controls) from 1977–80 and as a communications advisor for the Alberta Energy Company Ltd. from 1980–84.