"probably" walk off in Nadi due fatigue?
The tour of duty is so long that there is no option to "gas & go", that would cause the max allowed TOD to be exceeded. The IOC will be monitoring the weather and if it looks like the service may not make BNE, the intention is to pre-position a crew in the appropriate port eg NADI. This means a decision has to be made a day & a half ahead so that the crew can pax there and have the required rest period. Having close-in diversion ports such as Gold Coast and Amberley will help to reduce the number of diversions.
There has been a lot of work done before the services commenced so it should be a reasonably reliable operation - time will tell.