Edit:
Wait, what exactly did the kit come with? A full Z1 to Z2 upgrade disc? Or just the 30mb hacked upgrade disc for unlocking early Z2's (available freely on this forum, lol)?
If you were using the hacked "Z2 bypass" disc, it might not be too late. The disc only updates the HDD and should NOT make changes to or damage the firmware. If this is what you used, YES, you might still be able to save it with a fresh Z2 HDD image (either by buying a fresh HDD or by reimaging the drive). This thread has everything you'd need to know about reimaging your HDD.
However...
If you were upgrading from a Z1 to a Z2, I'm afraid there's nothing you can do. Ya see, the real upgrade discs write the new firmware to a cache on the HDD. The next time it boots it triggers the firmware update from the HDD, and as you know, if power dies here, so does your Z1. Similarly, if you're upgrading with a HDD image (as many of us have done), The files from the upgrade discs are already on the HDD, and the next time it boots, it starts the firmware update and doesn't know any different
I'm not certain if the Firmware updater cache is deleted after the firmware is updated. Frankly, I see no reason for it to be; During boot, it probably just compares whatever is in the firmware updater cache against your existing firmware. If they match, it moves on, and if not, it starts teh update. That's how it seems to work anyway. To confirm, I'd need to try taking a Z2 drive/image that has already performed the firmware update and placing it in a Z1. But I digress.
Whether or not the firmware updater cache is deleted or not is a moot point for you as the firmware on your Z1 is corrupt. Don't bother buying a pre-imaged drive because, cache or not, your firmware still won't be able to boot it. There is no recovery mode for partial firmware (that I'm aware of). Pioneer might have something else to say though. I suggest you call them.
The official CNDV700HD upgrade FAQ (Located here) states:
Q: The software installation process was interrupted and will not restart.
CNDV-700HD FAQ – Pioneer Electronics (USA) Inc. – 5/01/07
A: Please call the Pioneer Navigation Update Technical Support center at: 1-800-832-4227. (If you are in Canada, please call: 1-877-283-5901.)
Q: The Pioneer navigation system has no functions after installation is complete.
A: Please call the Pioneer Navigation Update Technical Support center at: 1-800-832-4227. (If you are in Canada, please call: 1-877-283-5901.)
Looks like you need to call Tech support =\
Good luck