Ignoring NZ's wishes for a moent, problem is either NZ leaving or Ocania combining with Asia leaves pacific football dead in the water. No-one is going to vote for that as Turkeys don't vote for xmas. Fact is pacific minnows have a far larger influence than they should do (they are tiny but also crap (as are we, but they're a lot worse) and really shouldn't feature in any sensible international competition at either club or country level) because of Oceania's existence so know having got that status they're unlikely to give it up.
GGW you say NZ has benefited enormously from presence in Oceania - yes to a certain extent but you also need to consider the counterfactual. NZ as a full blown member of Asia for the past 20 years might see us in a very different situation
Simple fact is though anyone other than NZ international teams or clubs representing Oceania at FIFA football events is a very bad look and won't be tolerated very long. That itself demonstrates that as a confederation Oceania is unsustainable in the long term in the current format