ugh, this is a rough spot to be in, turning it off may corrupt the update but leaving it on is useless too obvious. I think the only option in my opinion (maybe wait for Pioneer reps to respond too being they know more), is to reboot back into fw update mode, try a different formatted usb drive and re-download a fresh copy of the update in case yours became corrupt
In the service manual if you get your hands on it is a way to factory force the update even if it fails :)