Any shortage of NH-90 helicopters and too a lesser degree the AW109 within the RNZAF will take effect when they are eventually employed on the prime reason we bought them. Namely the tactical air support on a sustained Chp VII UNSC deployment rotation and would become critical when a short term Pacific event viz HADR or SASO Chp VIII type scenario compounds this. Where the issue will be at the crux point is the continuity of direct crew training and wider NZDF support and training whilst the RNZAF attempts to maintain the deployment rotation drumbeat and everything else will simply stop. Then along comes a flood, a blizzard, an earthquake or other natural disaster to fubar it all.
Not acquiring a simulator and other synthetic training for many years due to penny pinching held up crew TRADOC. The delayed IOC saw a significant number of trained crew leave during the types transition to service in that 2009 to 2014 period. Crews had to frequently go to Italy for a month or two at a time to conduct training and currency for many years. Huge delays in readiness for role in a number of areas of supporting equipment were also an issue. As for tasking tempo the significant cpfh of the NH90 has made the type less ubiquitous in the traditional supporting MAOT roles that the humble and low cost Huey did. In other words it is more rationed in its directed taskings.
The gap in the NZDF rotary exists in the lower end MOAT/HADR of the operational spectrum of what the NZDF is tasked to do. The thing to remeber is that the NZDF has a duality of key roles in its service to the nation as defined in the Defence Act. Armed Combat on one hand and the Aid to Civil Power on the other. One could argue that with 8 SeaSprites, 8 NH90's and 5 AW109 their is enough to cover (for now) the primary focus of sustained training and deployed support for a rotated UNSC Timor type deployment and in the case of the T/LUH direct competency training. The fact that over the current in service life that the NH90 has not needed to be used in that prime role is not an excuse to argue for the current levels of rotary assets to be acceptable. The non deployment status so far simply papers over the cracks. Once deployed the cracks will appear. However, acquiring a further fully fledged combat qualified MUH is not the solution. More NH-90's are not the only solution especially if a cheaper more appropriate MUH was acquired so that the NH90 could be freed up to do its prime role and not have to slum it rescuing farmers from the foofs of flooded houses. Deploying a LandSAR party to on a mountainside looking for lost hikers, lifting gas bottles and plastic water tanks for the Department on Conservation, flying a cabinet minister somewhere to inspect something!
The 5th option NG is of course to lease a Medium Utility Helicopter type that has an existing depot level support footprint to leverage into or at least buy them and retain a support contract within local aviation industry to reduce the RNZAF footprint. The 15 seat AW139 for example. The Australian Army has leased through Toll Aviation a small number of late to sustain capacity. A number of defence, SAR and law enforcement agencies world wise do this. The current commercial arrangement with Hawker Pacific with either a lease+support or acquisition+support reveals this way of acquisition not to be an issue. Especially for the roles in the lower end of the NZDF expected spectrum.
Guess we will just have to wait and see regarding the next major deployment to see if the govt will then go out and buy more helos, train more crews, build more hangers etc etc but then like you say they could just lease helo support to cover, either here or in theatre, as would still be cheaper than funding another fulltime fleet on a what if scenario. To use the Timor deployment again just reiterates the fact that any major deployment will be the primary focus of 3 Sqn, it was actually the primary focus of NZDF and actually stretched the entire defence force, army, navy and air force not just helos, everything, so going by that alone we should have increased numbers/capability in a few areas if that was actually the case as lessons were definately learnt from that op and in many instances the hard way. Perfect case and point right? But we did'nt, and that was over 20 years ago now so obviously somebody feels the current structure is sufficient, we have had the experience, we would run out of crews before we ran out of helos imo.
We do all these ex's to Aus such as Hamel exactly to test the ability to deploy in support of army, ie prime role, as well as every other deployment here and overseas to lessor degrees to prove the concept of deploying in the first place and the issue in my mind is not the number of frames more the sustainment and rotation of pers as we are not going to send over 6 NH90s to Timor just because we sent 6 hueys (which I think people believe) as that would literally require the entire squadron and the added capability of the 90 negate this anyway ie 2 90s would do the the job of 4 legacy hueys easily, so 3 NH90s would be a normal deployment in support. If Belgium? can deploy 3 frames to Mali for 6 months in the medevac role from their even smaller fleet then I'd like to think we could do the same, again the issue would be the sustainment rather than numbers. Hopefully we do a rotation (as rumoured) to prove or disprove the idea.
Yes agreed the NH90 cost (literally) overkills a lot of "minor" tasks now compared to.the hueys and defence will adjust their taskings accordingly but that's the price paid for the leap in capability and adding more 90s or another fleet would not lesson this. Perhaps just like the arguments for the axing of the IPVs will need to be applied and cheaper civilian options will now be required to conduct menial civilian tasks and defence shifts focus to core taskings? Even though to be fair even those tasks you mentioned all add up in terms of competency and training in lieu of actual "combat" flying.
The factor I feel that could possibly warrant any added numbers at this point would be the raising of the mooted bn group to 6000 "infantryman" (as the media puts it) but then a few capabilities and assets will no doubt require adding as a result so again will all come down to cost. Though I highly doubt this will happen any time soon as army is still bleeding numbers now, the reason there were so many loggies on the last intake was apparently because the supply trade is hurting with the amount of pers they are short, and that is just 1 trade! So while adding equipment is all well and good, just like a deployment, you have to be able to support it long term otherwise it is all for nothing.