I think autonomous trains per-se could work, but even then it would be worthwhile to employ the 1 driver that would even just sit there, as lives of 100s of people are at stake.
There are always "exceptions" to a ride, where a human driver / operator would help, such as a person hitting the emergency button because of a medical condition, violence at the carriage, someone's hand got stuck between the doors etc.
What should actually be is not autonomous trains as we envision autonomous cars, but rather sophisticated signalling and emergency braking automation.
In this day and age, I can't see how come a train is allowed to drive past a red light, depart a stop without supervisor permission or scheduled departure, exceed allowed speed etc.
These are very simple things infrastructure can enforce and I don't understand how come it has not been done yet.
I guess it has been done in some train networks. My personal familiarity is with the Melbourne (Australia) train network, and it's very old and untypical to a relatively modern western city.