That was my fear...my phone didn't start again after an official update that went wrong...
There is no other possibility in enabling USB debugging with adb for example ?
I'm stuck and have to erase all my datas...?:crying:
The first I do with a new device is enable USB debugging and check on OEM unlock bootloader cause mainly the first also sometimes can cause a bootloop on a wrong/failed update and to have more options in a worst scenario, take it like a lesson for the next time.
There are ways to enable USB debugging under adb commands but you will need su permissions for this, there are a way to flash a firmware through recovery using adb sideload but again you will need USB debugging and lastly in R5+ you can flash a rom through MiFlash Tool but in download mode so fastboot never worked for me on a Xiaomi with locked bootloader.
Try this last to see if it works, I don´t think but some time ago that I don´t use this tool, try flashing the same firmware that previously was onto your device using this tool on fastboot moed and checking in the centered option to flash and keep data at the right down of the tool.