I believe it is generally understood that none of the travel insurance policies would cover the CV-19 event. To the best of my knowledge, that has not changed, but I could be wrong. I am suspect of any resort or liveaboard that has a policy that suggests buy travel insurance for CV-19. That said there are valid reasons for travel insurance. Most folks tend to fall back on their credit card for some protection. In 10 years I have not had a single diver purchase travel insurance. I believe we are generally optimistic and believe "it won't happen to me."
Without "naming names" as you may know from following all the ScubaBoard threads, every resort and liveaboard has had different cancellation policies and the challenge has been for everyone, most policies have been developed assuming it is the individual scuba diver who is going to cancel, NOT the resort or liveaboard. Who would have thought...?
Now, in response to an event that is not the responsibility of any diver or resort or liveaboard or airline, many liveaboards and resorts have changed or modified their policies to accommodate guests, some have changed strict policies after a social media storm, and a few remain unchanged with the cancelation policy as "no refund."
As an agent, we are simply middlemen acting on behalf of our clients. We have no control over how a resort or liveaboard structures their cancellation policy, and the policies are probably developed by an attorney specifically to protect the resort or liveaboard. That said, our policies generally reflect those of the resort or liveaboard or airline. In case of extraordinary circumstances (like CV-19) I have personally offered to back my clients. Without my clients, I have no business, simple as that. I do not sell widgets or gizmos, I only provide a service and you either provide good service or bad service. There is not much in between worth talking about. Who wants service that is just OK...?
If a diver cannot or does not get to a liveaboard or resort because of a delayed or canceled flight, that is tricky. I usually recommend divers book flights that allow them a day or so before and after a trip. Flight schedules (domestic Indonesia) change often and if you book a flight that has a tight connection and miss that flight, the diver bears some responsibility and the consequences. And if this happens, generally a liveaboard will not hold the boat because a diver did not plan their flights to include possible flight delays or cancellations. The flights may be covered by insurance. Travel restrictions such as CV-19 are an entirely different animal that no one has foreseen. The best I can say is that most (but not all) resorts and liveaboards are trying to do the right thing by their guests.
If we have booked individual divers (not a group) on a liveaboard and the ship does not sail due to unfilled berths, I would expect the liveaboard to re-schedule the divers. I have never had a liveaboard not sail due to unsold berths so I have no past experience to relate.
If we book a full boat charter and as an agency, are unable to fill the berths, there are several options. Work with the ship to sail regardless of the number of guests is one option. Remember, as we are contracted with the liveaboard, I am obligated to pay for all berths if I sell them or not. That is my contract responsibility. So the liveaboard will get paid in full even if we only book two divers. Another common option you may see on ScubaBoard is to sell berths at deeply discounted rates to mitigate the agent's financial loss. I did in fact cancel one Raja Ampat charter a few years ago on the Arenui and returned the deposits to the divers and lost a non-refundable $4000 deposit for the full boat charter. So life as an agent is not all roses.
I hope I answered some of your questions. There is no simple answer that fits all situations especially with an event like CV-19.