AFAIK the only tax supporting AirNZ is the wage subsidy which has to pay wages (if was used to paid refunds would be fraud, additionally most AirNZ staff would be earning more than what the wage subsidy offers) and govt is underwriting charter flights for cargo and repatriation. Remember the loan is sitting in treasury's bank account, the terms of the loan introduce many strings which may/will make it more difficult to recover, so AirNZ hasn't used it.

The wage subsidy is for all businesses, don't think you can add more conditions after signing up thousands of businesses to the scheme

If cargo flights weren't underwritten many other businesses would fail as couldn't export. The amount of money left over after direct operating expenses will be minimal, not really enough to refund customers or support other activities. And chartering a flight is paying for a service not supporting the business.