As you already know, there are five ways of demonstrating a commitment to living in New Zealand permanently: INZ requires evidence of meeting only one of them. An 8-month absence will, without a doubt, result in you being unable to demonstrate that commitment by way of significant period of time spent in New Zealand. The other four options may be available to you, but I am unable to (legally!) tell you whether or not your circumstances will fit into one of them.
However, if you cannot demonstrate a commitment to living in New Zealand by any of those five ways, you may instead be eligible for a variation of travel conditions. And here, there is a special provision that you might fall into: a Resident Visa holder seconded overseas as part of their New Zealand employment may be granted a 24-month variation of travel conditions. See
RV3.20.10.
You may want to consider specialist immigration advice on this matter before taking up your overseas secondment. In particular, note that your secondment must meet the criteria at RV3.20.10(b) to be granted the special 24-month variation of travel conditions.