Whether the bump is voluntary or involuntary, the airline will arrange to fly affected passengers on the next available flight and will usually compensate them for the inconvenience. Whether the stranded passenger is holding a paid ticket or a frequent flyer award, compensation typically takes the form of a travel voucher, cash, frequent flyer miles, or some combination thereof.
A patchwork of policies
Strangely, considering that air transportation is widely acknowledged to be a critical part of the country's infrastructure, there is no single set of policies—either handed down from the DOT or agreed to multilaterally on the airlines' own initiative—that governs the treatment of airline passengers inconvenienced by flight irregularities.
Travelers who want to know the minute details of a particular airline's policies should look up the carrier's Contract of Carriage, the single most comprehensive policy document for any airline. In the digital age, all larger carriers have posted their Contracts of Carriage online, so they can be easily accessed and reviewed. The bad news is that Contracts of Carriage are not for those who are averse to small print and legalese. Delta's, which is by no means extraordinary, runs to 58 pages.
Or, for further inquiries, travelers can read the DOT's "Fly-Rights: A Consumer Guide to Air Travel."
Frequent flyers work hard to earn enough miles for an award ticket, and are by no means considered second-class citizens by any airline in the event of a flight disruption. Ultimately, the best consumers can do is know their rights, however limited such rights may be, and hope they don't find themselves in the position of having to invoke them.