What could be ahead for travelers and the airline after the Southwest holiday meltdown

More than a million passengers faced delays, cancellations or were stranded — or all of the above — during the holidays in what ranks as the largest airline operational breakdown in recent history. And many found Southwest's recovery not satisfactory.

But what are passengers' rights? What are Southwest passengers entitled to? What is the airline required to do? And what will they actually do? And, what will the U.S. Department of Transportation do?

The airline, facing the prospect of a huge enforcement fine from the agency, has publicly stated it will reimburse passengers for "reasonable" expenses. But Southwest has not defined "reasonable." In some cases, the airline has offered bonus frequent flyer miles to compensate passengers for their ordeal — hardly adequate, since so many Southwest passengers may only fly the airline twice each year, when redeeming those miles or points can be very difficult.