i'm having the same issue -- phone rebooted, bricked itself (wouldn't get past OnePlus logo), and now won't even boot into fastboot or recovery. PC recognizes device on COM4, shows Qualcomm 9008 drivers, but the unbrick tool stalls with Sahara communication failed error.
The sahara communication error and the firehose error can be fixed by holding down the power button and the volume + button for a few seconds.
I've got this entire process to work for me, but it does not unbrick the phone.
After it has completed the process tries to repeat itself.
The led is still light blue in colour and the phone does not respond.
What more can I do if the unbricking tool does not work and one plus is taking its time sending out the return label?