Possible in principle — trains can be utterly automated. But I seriously doubt that this means they will cease to be staffed. The calamities guarded against by PTC are not the only ones that locomotives can face. PTC won’t see an obstruction or other abnormal condition of a track.
It has been over 20 years ago, but when Rockwell-Collins was working with BN on the ARES program, one of my acquaintances on the railroad side would describe the features and accuracy they had already achieved and what was projected, and it was impressive. Still, he reasoned that without a human in the cab as one last safeguard, some situations were going to result in mayhem. His final take on it was, "The bean-counters will demand it, but thank God the public won't put up with it (a crewless train)."
I'm jaded enough to think that the public can be manipulated into demanding about anything.
Mr. niteowl77