According to the long-term stay policy of Airbnb, your stay would fall under this situation, where:
If they have more than 30 nights left in their reservation, only the next 30 nights are non-refundable.
Since, you'll be leaving on December 20, and it's only October 24th, there's still more than 30nights in between. Assuming you would change the reservation plan as early as now, you should get a refund for the cancelled nights.
Best option is to talk to your host as early as now, so they can also have their Airbnb calendar cleared and have a higher chance of getting it booked by other guests. Dawdling would likely give your host less time to have the cancelled nights book and getting that refund might be more difficult.