That is a good question.....
Does that mean the passenger must pay additional fare to the point they carried by to? And then to get back?
If not, that could mean that a few people might intentionally do it to save money when they book ticket....
And what if the next train back is a couple of days later in the case of a tri-weekly? Who takes care of accommodations, etc.?
And what if the passenger was asleep and the attendant didn't awaken the passenger? Who's at fault in that case on an overnight train during the 'wee' hours?
Lot's of what-ifs to consider...
I'm no expert, and I've never experienced a 'Carry-By' before, but I'll take an educated stab at what happens.
Depending on just
how a carry-by occurred, in most cases it could very well incur an additional charge to the offending passenger. It would be entirely up to the conductor, of course. In the case listed above, it sounds like there was ample time and warning given for the stop that was missed by this one individual.
For the accommodations, that would probably be on the shoulder of the passenger. They would need to get ahold of Amtrak, and change their reservation to embark at an earlier station than originally reserved. Or find transport to the original station. Either way, probably going to pay more.
With e-ticketing and electronic, real-time manifests now in use, missing a passenger in the middle of the night in coach is less likely. But it could still happen. There is still a bit of responsibility on the part of you, the passenger. I always set an alarm if I know my stop is in the middle of the night, even when I'm in sleeper. Worst case scenario at that point is the train is running late, and you wake up early.