If Vernon loses, I expect Pat Murphy will run in 2018 or 2020.
Patrick Murphy of Pennsylvania may run for Congress again, or he may remain Secretary of the Army/become Secretary of Defense.
Murphy from Pennsylvania's future definitely lies in the Pentagon; he's Under Secretary of the Army at just 42. A very plausible career path would be moving up to Deputy Secretary of Defense (IIRC, multiple DSoDs have taken this exact career path) and staying there for a few years before becoming Secretary of Defense. He could very well be SoD before age 50.
Even if Hillary loses in 2020, even twelve or eighteen months as Defense Secretary would set him up perfectly to run for office later.