Worst case scenario? Three guys armed with a paper aeroplane, a F.R.E.D. and a rubber ducky respectively.
More realistically, I suspect that further erosion in NZDF capabilities, or even just the perception of further erosion in capabilities, will lead to a diminished Kiwi presence on the international stage, with a correspondingly diminished relevance accorded to Kiwi interests, opinions, and perspectives. In short, the views of other nations' regarding NZ could to the point where Kiwis are considered nice blokes, but otherwise irrelevant.
A hypothetical example of what I mean would be something like a natural disaster and/or civil unrest occurring in Fiji or another S. Pacific or ASEAN country that requires or leads to an international intervention. If the NZDF capabilities are viewed as too limited or too eroded compared to what is needed or desired, then NZ might find itself without a seat at the table when plans and decisions are being made, as well as without a presence on the ground, offshore, or in the air above where the intervention is occurring, and therefore unable to impact the outcome in any way that is either favourable to NZ, or at least not to NZ's detriment.