@Owner-Nancy--Todd-Manage0 Wow, that is an incredibly unlucky year for guest health issues! I hope your 2020 goes much more smoothly.
I think it's good hospitality instincts inspiring you to feel concern for your guests when they're unwell. However, it's also a degree of risk that it may not be realistic to take on. If someone's health circumstances change during their stay and your property is no longer safe or suitable for them, the best thing to do would be to contact Airbnb for assistance with relocating them to a more appropriate accommodation. (This would also be the case if upon arrival you discover that the guest has a disability that you can't safely accommodate, such as a wheelchair in a tree house).
As for the guest's who disappear for several days during the stay - their booking is still valid until they check out or cancel, so from the accounting end of things it's not an issue if they aren't actively using the home. But from the hospitality perspective, I think it's good to give guests the option of supplying an emergency contact number upon arrival - especially if they're engaging in outdoor sports or appearing to be of an age or condition that might be considered high risk. I stress that this must be optional and not required, due to privacy concerns. But if a guest is incapacitated during their stay, it would help you out to be able to pass the torch to the person they trust most to act on their behalf.
Also, of course it's best to keep precise records and an up to date paper trail within Airbnb when a booking involves an emergency. Every detail counts when liability claims come into the picture.