[Moto Z Questions & Answers] bullfinch110:
I asked a honourable friend to look at your problem. Here's his answer:

"Hmm, I've been thinking on his issue and it looks like the member will either need the fastboot 7.1.1 griffin stock ROM or have to visit the service centre.

The stock ROM is there if the member needs to re-flash 7.1.1, as it sounds as though something happened with the OTA update - either it didn't complete properly or a partition is damaged. However, looking around, it looks like Motorola has not released the fastboot ROM (or someone hasn't captured it yet), so it may require a visit to the service centre, as you've suggested. They may charge to re-flash the 7.1.1 stock ROM, if they have a copy. Unfortunately, as the member's pointed out, the warranty for the Moto Z they've bought isn't valid in Argentina :(

The current path I can see is the one you've suggested - as they cannot unlock their bootloader (as they can't boot), then the service centre is the only path so far. I'd suggest asking them intially to re-flash the 7.1.1 firmware if they have it - as 7.0 won't work. If not, they may replace the motherboard (I don't know if they'll charge given that it's a fault that the update brought, but it's not a device in their jurisdiction"

Edit: Before you visit a service center lets try a last attempt by flashing another firmware...

Download this one and extract it like you did before.

https://www.androidfilehost.com/?fid=961840155545594425

Modify its flashfile.xml by deleting the "gpt" line. Flash with RSD-lite.

If it'll fail again, try the ultimate last attempt:

Not sure if the minimal adb fastboot method works without having usb debugging enabled...

Download and install minimal adb from here

https://www.androidfilehost.com/?fid=745425885120698566

Copy the extracted firmware into the same folder, where you've placed the minimal adb file.

Run the minimal adb fastboot program...a command window should appear.

Connect your motoz in bootloader mode with your pc. Type: fastboot devices. If it shows the serial number of your motoz, proceed by typing the following flash commands one after another:

fastboot flash modem NON-HLOS.bin

fastboot flash fsg fsg.mbn

fastboot erase modemst1

fastboot erase modemst2

fastboot flash bluetooth BTFM.bin

fastboot flash dsp adspso.bin

fastboot flash boot boot.img

fastboot flash recovery recovery.img

fastboot flash system system.img_sparsechunk.0

fastboot flash system system.img_sparsechunk.1

fastboot flash system system.img_sparsechunk.2

fastboot flash system system.img_sparsechunk.3

fastboot flash system system.img_sparsechunk.4

fastboot flash system system.img_sparsechunk.5

fastboot flash system system.img_sparsechunk.6

fastboot flash system system.img_sparsechunk.7

fastboot flash system system.img_sparsechunk.8

fastboot flash system system.img_sparsechunk.9

fastboot flash system system.img_sparsechunk.10

fastboot flash system system.img_sparsechunk.11

fastboot flash system system.img_sparsechunk.12

fastboot flash oem oem.img

fastboot erase cache

fastboot erase userdata

fastboot erase customize

fastboot erase ddr

fastboot reboot

I hope someone could correct me if i'm wrong or provide better help. If not, maybe you'll have success by visiting the service center.

Good Luck!