This may be helpful:
http://www.airfarewatchdog.com/pages/18939347/Cancellations Within Airline Control
If, for any reason, a passenger’s Southwest flight does not operate as scheduled, Southwest Airlines will, at the passenger’s request, refund the unused portion of the passenger’s fare or will assist him or her by arranging transport to the passenger’s destination on another Southwest flight with available seats. If the passenger elects to take an alternate Southwest flight, he or she will not be charged any more money even if the ticket for the disrupted flight has usage limits or fare restrictions.
If circumstances within the airline's control cause a passenger to miss the last possible flight or connection of the day to his or her destination, Southwest's customer-service agents have the authority to arrange for overnight lodging for that passenger and will find the passenger a hotel or motel as near to the airport as possible, at no additional cost. Customer Service may also arrange for ground transportation to the overnight facility.
