If someone who is expected to go somewhere fails to go there, you can say that they are a no-show. At my wife Lucy's fortieth there were two no-shows, and two people called up to cancel after the party had started.
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Some airlines include a no-show clause in their Contract of carriage. It basically means that a user not showing up for the outbound flight will be considered a no-show, and all the connecting flights associated with this one, even a return flight, will be cancelled and no refund will apply.