No, we used frequent flyer miles for our airfare. But it's my understand that they will cover you for rebooking regardless of how you booked in the first place.
The last time I called, they told me it was about 25% full. Which surprises me that you still got an early booking discount. We also picked this one for the discount. We really wanted the [Adult only] one leaving 3 days earlier. Then we figured you can have annoying adults just as well as annoying kids, so the discount won out!!