Re the cost of diversions I'm sure the airline pays for it but I don't know whether it can be claimed back from the airline's insurers afterwards [?] So long as the crew don't go out of hours or anything then the costs would be restricted to the extra fuel + landing/handling charges + possibly welfare costs if there is a significant knock-on delay.
There are a few places on the east coast of Canada that we occasionally use for medical emergencies, these being Halifax, St. Johns, Gander and Goose Bay. The rest of the pax stay on during diversions...it generally takes about an hour due to having to find the passenger's luggage etc.
Cheers
Alan