If a railway line is closed and the roads are open then you can just throw the freight onto trucks. I don't understand how you read an article suggesting we diversify the network onto coastal shipping and rail, and think that means we should ban the current methods. But rail is also more resilient than roads because it's raised out of water, no pot holes, crashes are rare (and almost always vehicle vs train, which can have rail operating again pretty quickly), less affected by slow traffic. Getting a larger portion of long-distance freight onto rail will also improve things for other road users, in terms of less traffic, and moving more heavy freight onto rail will also be a huge benefit in terms of pot-hole prevention.

The only argument against rail that I can think of is that it would require hubs for loading/unloading trucks for the first and last mile. But in terms of Auckland/Wellington transport rail seems like a no-brainer, when currently there are probably thousands of trucks making the trip each day.