@Jody136 I can't see Airbnb giving some firm date for extensions- they've just been playing it as it comes. It's the guest's situation that is driving the cancellation, so it's the guest who should just go ahead and cancel and cite COVID19. It sounds like you are amenable to a full refund, so if the cancellation doesn't result in that, you always have the option to reimburse the guest through the resolution center. But wait til you get paid first.
The sooner the guest cancels, the sooner your calendar opens up and you'll have a chance to rebook the dates.