Hi there, Amanda!
Amanda, you are right that if you want to fly high on a Banshee on
Pandora - The World of Avatar, and explore the savannah on
Kilimanjaro Safaris, you will need a valid
Disney Park Pass system reservation.
While I wish I could travel back in time like on
DINOSAUR and snag a reservation for you, we do not have any information on if unused Annual Pass reservations will be redistributed to other groups of ticket holders.
What I can tell you is that the Disney Park Pass system is updated in near real-time, so as people rearrange their plans, you may luck out and pick up a last-minute reservation. So, my number one tip for you is to keep checking!
If there is availability for another park on that day, you can also upgrade your theme park ticket to add-on the
Park Hopper Option. This will let you start your day at your reserved park, hopping over to Animal Kingdom at 2:00, as long as it has not reached capacity.
I hope that this gave you a bit of hope, Amanda!
Good Luck!
Sarah B.