You are jumping way ahead - although I understand why you need to...
If a guest gets stuck at your house then you either put them up out of the goodness of your heart, as they are stranded just like you, or you ask them to pay for the additional nights.
You should not make the decision to cancel - your guests should. Othewise you will be penalised.
No harm in warning them to keep an eye on the weather and plan their travel accordingly.
If you find your property is cut off or dangerous to access around their arrival date then contact AirBnB and let them make alternative arrangements for your guests.