Even if there is a delay they don't say they will pay all the costs of getting you to the next available port.
[Quote from HAL's Flight Ease FAQ:]
"Late Arrival Protection
Should guests who have booked their air travel through Holland America Line experience delays en route due to a flight delay or an airline service disruption, such as flight cancellation or flight re-routes, that will cause them to miss their original port of embarkation, Holland America Line will work with the airline to find reasonable alternate flights to the next appropriate port at no additional air cost to the guest.
Factors taken into account in determining the appropriateness of a port of call include, but are not limited to:
where in the original itinerary the port is located
airport / port infrastructure
visas and other legal documentation that may be required
application of the Passenger Services Act to the new itinerary
comparability of cost, flight connections, and travel time required (any unused value on the original air ticket will be used to offset the cost of the new air ticket)
Liability and Relation with Airlines
As the airfares we use are based on capacity controlled, promotional, and group fares, we may limit or close sales without prior notice at any time. If, due to any cause beyond our control, we are unable to arrange for air travel or the air travel we arrange is unavailable or otherwise fails to materialize, our sole liability will be limited to refunding the air price paid to us. We assume no liability for any acts or omissions of any airline, including, without limitation, those involving cancellation of flights, schedule changes, re-routings, damage to or delay or loss of baggage, flight delays, equipment failures, accidents, pilot or other staff shortages, overbooking or computer errors. The liabilities and obligations of an airline to you, and your rights against an airline, are subject to any and all terms and conditions of the airline's ticket and tariffs and all applicable governmental laws and regulations.
[End Quote]
So HAL will "work with" the airline to get a "reasonable alternate flight" to the next appropriate port of call and if they cannot find that all they are obligated to do is refund you and that's it. No hard guarantees.