Hi Rebecca, and welcome to the Disney Parks Moms Panel!
The Walt Disney World Resort is all aglow during the holidays, but of course all good things must come to an end. While I don't have any official word on when the Mickey ornaments, Christmas trees and garland will be put away for the year, I can share my personal experience with you.
We visited Walt Disney World last year for my birthday, around the second week of January. Even though Santa was long gone, it was still feeling a lot like Christmas around the Theme Parks! We found that most of the holiday decorations remained up in the parks until just after the Walt Disney World Marathon Weekend. If they keep to that schedule this year, we may see Christmas linger through Marathon weekend on January 6-10, 2016.
While the Theme Parks may still be decked out for the holidays well into January, the holiday-themed events and most of the decorations in the Resort hotels should be mostly wrapped up right after New Year's Day.
Do keep in mind that although last year's schedule is a handy guide, it could certainly change in the future. Thanks again for stopping by, Rebecca, and please come visit us again if you have any more questions!
Keep Disney Dreaming,
Kathy K.