If fares go down, Southwest will allow you to rebook at the lower rate, and carry the difference as a credit into the future with no change fees. You have to use the credit within one year of original booking. You used to be able to combine different people's credits into one ticket. I booked 5 tickets to San Diego last fall for a March trip, and when the prices went down by $70/ticket a month or so later, I rebooked and was able to use the credits I received from the family's tickets to buy a $350 flight for a later trip of mine. Southwest was going to change that so that only the person who booked the original ticket could use the credit, but I'm not sure if it's gone into effect.