Following his basketball career, Wintermute worked for Boeing. He was elected to the Oregon Sports Hall of Fame in 1980. On October 21, 1977, Wintermute set out in his yacht from Portage Bay in Seattle's Lake Union and did not return. His boat was found a few days later, with one of Wintermute's friends asleep on the boat who claimed that Slim was still alive when he went to sleep. Wintermute was never found.