In the unlikely event it happened during the life of the mines I...

In the unlikely event it happened during the life of the mines I don't think it would spell commercial disaster if company collapse is what you mean.
If production had to cease for a period of time costs could be reduced very quickly. Force Majeure would apply to contacts in place, including supply and transport, the workforce could be scaled back and leave taken etc machinery running costs would virtually cease and the company could no doubt survive.
A stockpile at lyttelton would however significantly reduce the impact.