@Kathleen710
With "long term stays" only the first installment is guaranteed, as reservation can only be confirmed when the guest pays for the first month. If the guest does not pay next installment, Airbnb useally sends a message "we can not collect the money" but they have no force to charge the guest (That's why some hosts use an extra lease contract for long term stays)
If the guest cancels, they still need to pay for 30 nights (dictated by the "long term stay" cancellation policy).
As a host you can shorten the reservation ("change" option) to a new check-out date and also you have option to amend the price in the pricefiled to what you consider a fair deal.
BTW
If the guest can pay only 2 weeks and you trust the guest then after 2 weeks you can change reservation again by extending it.
With "long term stays' host sometimes must be creative....