Hi Jennifer and welcome to the Disney Parks Moms Panel.
You are quite correct in stating that the hours to
Meet Merida at Fairytale Garden at the Magic Kingdom park are only available to view for dates up to and including December 17, 2016 at this moment in time.
I haven't seen or heard anything to suggest that Merida will be ceasing to meet and greet with Guests at this location and quite often, you will find that the hours are only available to view on the Walt Disney World website approximately 1 month in advance for these type of encounters.
My best advice to you would be to keep checking the Walt Disney World website frequently between now and your arrival at the Walt Disney World Resort to check if hours have been added for dates after December 17, 2016.
Alternatively, be sure to pick up a Times Guide as you enter the Magic Kingdom park to see if and at what times Merida will be meeting and greeting Guests at the Fairytale Garden on the day of your actual visit.
Wishing you a magical trip filled with memories which will last a lifetime!
Emma