Dempster was named a delegate to the 1956 Democratic National Convention in Chicago, although he largely retired from city politics after his defeat in 1955. He later rejoined his old nemesis Cas Walker in a successful attempt to thwart city-county consolidation, which was soundly rejected by Knoxville and Knox County voters in a 1959 referendum. Dempster died of a heart attack on September 18, 1964. Over 1,000 mourners, among them US senators Al Gore, Sr., and Herbert S. Walters, crowded into the St. James Episcopal Church for Dempster's funeral. He was buried next to his wife in Greenwood Cemetery.