Here I've got two Redmi 5 Plus with the exactly same problem: android don't boot.
The last word of both phone was: System has been destroyed.
If you connect the power cable the white led flashes and the screen remain off.
If you press and hold [Power and Vol-] nothing happen, same as [Power and Vol+].
So you can't use any fastboot or adb command.
So I've opened the phone.
I've disconnected the battery and the fingerprint scanner.
I've installed all the divers needed.
I've connected it to my pc in EDL mode with testpoint.
The phone is correctly detected as Qualcomm HS-USB QDLoader 9008.
I've downloaded the last version of Mi Flash I've find (MiFlash20191206).
I've downloaded different Fastboot ROM Global. (vince_global_images_V10.2.1.0.OEGMIXM_20190325.0000.00_8.1_global_a6f1d912aa.tgz)
When I try to Flash MiFlash say [ping target via firehose] and than [write time out, maybe device was disconnected]
I'm stuck here.
Can You help me please?
In order to fulfill the basic functions of our service, the user hereby agrees to allow Xiaomi to collect, process and use personal information which shall include but not be limited to written threads, pictures, comments, replies in the Mi Community, and relevant data types listed in Xiaomi's Private Policy. By selecting "Agree", you agree to Xiaomi's Private Policy and Content Policy .