@Charlie48 well, that is always a possibilty even if you book a hotel. But, hosts are punished if they cancel so it doesn't happend often on Airbnb
But in case it happens you will get your money back in few days so it is always good to have some extra money on your credit card while you travel, just in case you have to book another room in the last minute
And if a host does decide to incurr all those penalties upon themselves, and esp. if it's very close to your arrival, then Airbnb is often able to help you find an alternative. Keep their phone no. on hand (either on your booking confirmation or Google 'Airbnb phone Australia<.