April flight cancellations should be loaded at the end of February or early March. At that time, assuming SFO-AKL on UA metal is cancelled, OP's friend can ask UA to rebook them on NZ, though that may not be possible due to availability or other reasons. Not sure whether they are booked on an award/upgrade or a revenue fare; the latter should be easier for UA to rebook on NZ, but is NZ revenue J really sold out through July?