I have heard a rumour that the NZ MHEG5 EPG data is to be discontinued although I don't know what the timeframe might be. It's probably tied in with the introduction of FreeviewPlus.
Some terrestrial users have already had to switch to different frequencies to collect EPG data and this may be the first step in the process.
The good news is that 7 days of EIT data is now being broadcast on terrestrial. I don't know if it is for all channels and the text is encoded in the same way as UK FreeSat (so if you use EPG Collector you need to set the 'Use FreeSat Huffman tables.... ' option on the Advanced tab to decode it) but it maybe worth trying a 'test' collection to see if it works for you rather than waiting until the day the MHEG5 data disappears.