Hi
I recently had a similar situation. Some guests damaged my double sofa bed ( brand new leather ) situated in the lounge/living room.
As the sofa/lounge had to be taken off site to be repaired, I emailed all my guests to let them know I was down 1 bed. Most were fine with this as it was something out of my control.
One guest however insisted I cancel their booking, as I had advertised a certain number of beds which was now not going to be available to them. I explained that I was still able to host them, as the house has plenty of room ( I could of supplied a floor mattress or something similar) and there was ample seating. However, they contacted airbnb and airbnb (without speaking to me first) cancelled the booking on my behalf.
Once cancelled I was given opportunity to send photos and give explaination ( all which had already been processed through the resolution centre and payment had been claimed and made)
I was told I would not have to pay any penalites, given this was my first cancellation and I am only a few months into the airbnb hosting experience.
However I am now unable to have anyone else book the dates that were cancelled as airbnb have blocked these dates.
So it looks like even if you have extenuating circumstances, the host will still be penalised.
Guess it's all a learning experience!