What happens if you don't show up for a flight?

My wife recently bought a one-way ticket that, due to a change in schedule, she will not be able to make. The ticket cost less than the cost of a change fee, so she is going to abandon the ticket rather than move it. The airline rep (I forget the airline, think American or United) said it costs $150 to cancel a ticket (the ticket cost less than this).

What happens if she just doesn't show? We fly this airline with some regularity.

On a related note, what should one do with a cheap ticket (less than $150) they can't use, other than abandon it, when the change fee is $150?

Although policies differ by airline, United generally will allow people to refund tickets if there was a schedule change of greater than 90 minutes (I wasn't sure if you meant that your wife had a change in HER schedule, or if the airline changed the schedule of when its flight would operate), or at the very least they should be willing to allow you to change the flight to another time or perhaps even another day.

If you just don't show up for a flight, at midnight the ticket will "zero out" and have no value. Since your ticket is worth less than the $150 change fee, you're fine with just "no-showing" or you can ask them to cancel your reservation (not cancel the ticket--this is different). The only reason you might want to cancel the reservation is out of courtesy to the airline, but many people no-show, so you should be fine with just doing that if you want, too. It won't cost you anything to cancel a reservation, but this is different from refunding a ticket (i.e. you won't get any money back).

Nothing will happen. Since your wife won't check-in for the flight she is just one of thousands of no-shows. Airlines know this and its part of their daily operation

Is there a limit, how many no-shows somebody can have on a ticket ?

I guess so, since the ticket has usually a limited validity (d days) and there are only so many flights per day (f). The maximum number of no-shows on the same ticket would therefore be d*f.

HTB.

nor do they care as its free $$$. However this is way different from not flying the last segment a/k/a Hidden City

You are right but in the case the OP describe I don't see any last segment Hidden City problem. There is even no problem with a return flight since it is a one-way-ticket.

I was one of many who had passport renewal problems last summer, and I became worried that I might not be able to take my flight to LHR. I went to the airport to talk to a real United customer service rep face-to-face (not wanting to hazard the overseas call center). She told me that if I was unable to take my scheduled flight due to passport problems, I should call United before midnight and explain. This would keep my ticket valid for a future trip. If I did not report my problem to United, the ticket would vaporize at midnight.

As luck would have it, my passport arrived the day AFTER my scheduled departure, but since I had notified United, I was able to rebook and get squeezed onto the last possible flight that would allow me to attend the conference that was the purpose of the trip.

I'm interested with this topic. I have problems previously which I bought a return trip and put a no show on the return trip. I purchased another one way trip to complete my trip. I wondered how about the opposite which I won't be able to make it on the departing part of the trip, will I be able to use the return part of the trip.

It may vary by airline, but in most cases, if you no-show for any part of the trip, all subsequent flights on that reservation are cancelled and the ticket value is lost.

Most cases has to be read as: almost all cases (I don't know of any differences, so I even should say: in every case).

So missing the first segment means a cancelled ticket.