While a two person crew might not be necessary on a freight train under certain condition, how about Amtrak? There is a big difference between a 14 car passenger train and a 150 car freight train yet the Amtrak train crew consists of an engineer, an assistant engineer on some trains, a conductor and assistant conductor.
With the elimination of onboard ticket collecting and reporting, I would think Amtrak would be better served by eliminating the ATC and replacing him with and an board crew chief that would be responsible for assisting with on board services and, most importantly, insuring proper training of the OBS staff to improve service consistency. In an emergency he would be authorized to assist the conductor and would need to be qualified on the book of rules. This would be more like VIA service where I believe the train crew has limited if any customer interaction. There would be no reduction in crew size but a better use of the crew to improve passenger satisfaction.