Maybe u need emergency solution:
1) download this, this is the aboot partition of the 7.2.4.0 which the fastboot mode still can access the edl mode:
https://drive.google.com/file/d/0Bx3JyADgcb...ew?usp=drivesdk
2) reboot ur phone to fastboot mode
3) at ur pc with fastboot access provided, type this(this one can be flash even in locked bootloader):
fastboot flash aboot emmc_appsboot.mbn
4) reboot ur device to fastboot again with this command:
fastboot reboot-bootloader
5) type this command, see the “bootloader status” got appears or not:
fastboot oem device-info
6) if got then type this, as soon as u type, press and hold vol+ and vol- button together.
fastboot oem edl
7) assuming you had already installed mi flash, your pc is able to detect as the Qualcomm loader with COM port show, download ur fastboot ROM and put to Mi flash to flash, remember to select flash all script and "flash all" before you flash