How about (in the case insurance is not available or used) mid-flight hardware failures? Is the responsible party the owner who never sees or maintains the drone, the user who only request services and does not own or operate the drone, the charging pad owner who launches the drone, or the platform that facilitates the flight?
Very interesting question, I guess you are not the only one having these kind of legal questions in the drone domain. I'd say : like for car insurances, drone insurance should be mandatory. Seriously.
But in case it's not, well... courts will have a lot of work.
Anyway, looking forward to seeing your list of countries!