Upvote:1
The Immigration NZ web site is clear, as you have discovered: your visa expires when you leave New Zealand.
However, you can return to New Zealand with a visa waiver provided you do not stay more than six months in a twelve month period (Source Enter your details and select Visa Waiver Visitor)
After 1st October 2019 the eTA scheme comes into play. Details on the same link as above. You can return to New Zealand within two years and get a second visa.