The fact that the 'tyranny of distance' does indeed cut two ways, yet most people seem to not realise/ignore that fact, is one of the issues I have with how many people approach NZ defence.
NZ is potentially vulnerable to events which are not even directed at it, but could still become 'collateral damage'.
As for the hostile sub off the East Coast, I would not worry too much about that. Unless the AB's really do a number on Australia, then all bets are off...
On a more serious note, while such an event is not likely, given the projected expansion of sub forces operating in the S. Pacific and ASEAN regions, it is certainly NOT impossible. Which is part of the reason why I have had some concern on the viability of the NZDF in ASW ops. While the P-3K Orions, as well as the Anzac FFH's have some ability to perform ASW, they are likely to run into a number of difficulties. The first, and potentially most major issue is the NZDF stock of LWT's. IIRC the NZDF has a stock of either Mk-44 or Mk-46 LWT's, which according to the LTDP were going to start, or perhaps completely expire in 2008. I took issue with that when I came across it, since according to the LTDP, the torpedoes where expected to be replaced in 2015. While I do not know for certain, and perhaps a current/ex-Navy servicemen could comment, my understanding of what it meant when a munition expired, was that in this case, the torpedoe could be launched/dropped, and then it might operate normally, or it might not, or perhaps even be a dud. That is something which IMO needs to be rectified ASAP. While the frigates and MPA have issues due to sensor and electronic fitout, which could make detection of modern diesel-electric subs problematical, that does not matter much if the aircraft of frigate cannot engage a hostile contact which is detected because the munitions are too old to function as required.
-Cheers