New Zealand have only done a great job until a vaccine can be proved to work, and can eliminate the virus. Until then, all they are doing is being good at keeping it out, and fair play for that, but they are in a far better position than we are/were.
If they want to ever return to normality, and start visiting the rest of the world, and have the rest of the world visit them, they will have to reopen, and unless the virus has been eradicated it will inevitably get back in. It's summer there now (or soon) so that helps, but after every summer, winter follows, so lets see where they are in 6 months time.