I personally strongly urge any traveller to purchase some form of medical coverage when travelling, whether by land or water! As an example, I'll recite my experiences in 2012.
Doing a land/cruise with Holland America in Alaska, I contracted pneumonia just prior to boarding the
Zuiderdam in Skagway. On-board medical personnel rightly diagnosed my condition as one which should/shouldn't be treated on the ship.
Bottom line: Medival evacuation expenses in addition to hospital costs in Juneau amounted to very nearly $50,000. My purchased medical emergency cover, bought from the cruise line, covered virtually everything with essentially no out-of-pocket costs from me!
SWR