Anyone at any time can cancel using extenuating circumstances and as the host you just have to eat the cost. I had guests who were coming from several states over Thanksgiving (high dollar holiday). In states where some of the guests lived it snowed. It did not snow at my property. None of the guests showed up even though they kept indicating they might come depending on the weather. After their scheduled stay was completely over they contacted Airbnb and cancelled and Airbnb recouped their entire rental amount from me.
I, of course, could not rent the property to anyone else because the guests had a paid valid reservation (with strict cancellation policy) and had the ability to arrive at any time during their scheduled stay. For them to cancel afterwards because they did not actually show up and for Airbnb to refund them in full is unconscionable.
Hosts, beware. Airbnb can arbitrarily cancel any reservation for any reason, even after the reservation has ended, and fully refund the guest and you will receive nothing.