Last year when ComAir went on strike, Delta changed our flights w/o a problem. In fact, they let us decide when we wanted to go. We opted to fly out a day earlier than originally scheduled because the flights offered as an alternative left too late in the day. The return flight was also changed permitting us to swim and relax prior to our flight AND still get home at a reasonable hour. We had two "down" days at BC where we could relax after all of the park hopping the prior 8 days.
This year, Delta again changed flight times for our return leg. The newly adjusted times would not allow us to make our connection in Atlanta. Because of this, Delta gladly let us change our flight times and we opted to go out the next morning rather than leaving earlier in the originally scheduled day. Now we will have a full day in WDW, head to the airport hotel to sleep, and fly at 9:00 a.m. the next morning. We will also be returning home at a very reasonable hour in the afternoon.
Our original flight would have required us to leave WDW around 3:00 p.m. and we wouldn't get home until midnight! All-in-all it's a much better deal for us flightwise. In fact, those options would have cost us considerably more than we paid for the originally scheduled flights!
Saving money, getting more time in Disney, and having agents that handled it without complaint and cheerfully! Delta's been great to us.