Update: Airbnb replied a few hours after my post to the Community, with an assigned case manager.
Her name is Cynthia. We corresponded multiple times via email. She also reached out to my guest who was scheduled to check in the same day and refunded all her money.
Because resolution of my issue (replacing my old 18,000 gallon water catchment with a new one) is going to take until the end of this week, she cancelled my next guest that was due to check in tomorrow, actually.
I sent her pics to document the sad state of what was left of my old water catchment and Cynthia sent word back that that was good enough for them and Airbnb would not penalize me.
So that's the gist of it all. Lots of stress, running around, calling many merchants, driving to the bank because various merchants wanted cash with short notice and emergency priority status, emails to Airbnb, responses to two concerned separate Airbnb guests, and...lots and lots of money going out in a way we did not plan.
Airbnb 'help' was great, although a couple worrisome hours when I didn't realize that my case manager was not replying to my emails because she had already clocked out for the day. But she did respond. And she had my back. And, that was very comforting. To myself, my husband and to my two Airbnb guests who needed new places to stay.
Thank you, community for your support and your guidance.
Thank you, Airbnb for having my back.