In my mind I have sort of a list of the possible misfortunes I can think of that might impact a dive trip, my vague guess at their probabilities, and my vague guess at the cost I might suffer as a result. (I also keep in mind that insurance companies know all of this with much more accuracy, which is why they find it profitable to sell us insurance.) Things that are low probability AND low cost aren't worth insuring to me. Missing a single day or even the first two days of a land-based resort isn't that costly as I see it. In hundreds of trips I have taken, I have never gotten sick at just that point in time at which it would have prevented me from diving for essentially the entire trip; I think that's a low probability. I can choose a liveaboard with a policy of awarding vouchers for canceled trips, which, while not an optimal resolution, is still worth something to me, as I'm only out of pocket the airfare, and in a lot of destinations I can probably still salvage the airfare by doing some land-based diving or sightseeing. I can lower the probabilities of some events by arriving two days early, leaving 5+ hours of time for international air connections, and those sorts of things.
The ONLY event I have been able to come up with that I perceive as being high-ish probability AND high cost is missing a liveaboard departure due to an (all too common these days) airline snafu, where there is no way at reasonable cost to catch up by boat with the liveaboard at sea. I wish I could buy insurance for only that. As I have said before, being reimbursed a few dollars for dinner and lodging while I wait for an airline to "allow to resume onward travel" is not what I consider a cost major enough to insure against; I am willing to count occasional relatively minor (compared to a $5000 liveaboard) costs like that as part of the cost of travel these days.
On an unrelated (I think) note,
@outofofficebrb : when I plug numbers into those online insurance quote generators, should I be including the total cost of the trip, including airfare, the liveaboard/resort, side trips, and whatever else I have paid in advance? It occurs to me that an event that would trigger reimbursement of airfare AND diving--that is, the whole trip being canceled--would have to be limited to something like a major sickness or injury occurring soon before the departure date. That seems unlikely to me. More likely would be something like I mentioned above, where I miss only part of the trip. Why could I not plug in a smaller number of my choosing, so that I'm effectively capping my own reimbursement in order to lower the premium?