[G4 Q&A, Help & Troubleshooting] Mejilan:
Well, I'm at wit's end. I'm usually pretty decent at borking and consequently unborking a phone. But I think I'm stumped this time; and am hoping that the community here can help me out. Though, to be fair, I suspect that rolling back to my old phone and eventually buying a new one is my only recourse.

So I imported an H815 Open EU from Handtec UK. No real issues on that front. I eventually unlocked the bootloader, flashed TWRP, and used the KDZ method to (clean) flash my way up to Europe OPEN H81510D initially, and then around two months ago, to Europe OPEN H81510E. I've been running that software without issue since that clean flash. And all this time I've been rooted through the TWRP method.

While this is (was?) my first LG phone, it isn't my first Android experience. So I've been using TiBu to back up my apps nightly, was running Kickoff's lovely hybrid theme, and had a few Xposed modules activated to tweak my experience a bit from stock behavior. I was curious about Marshmallow, but autoprime's warning that it could be non-final test software and the fact that Xposed doesn't work on it kept me from indulging that curiosity.

Everything has been going swimmingly until today. No major issues that I couldn't solve on my own. Certainly nothing that booting into recovery and clearing caches didn't fix. I was out and about engaging in a chat via Hangouts with a friend when my phone suddenly crashed and black-screened. I wasn't plugged into the wall or my PC, and I hadn't performed any kind of major update since the 10E flash a month or two ago. I had not installed any new Xposed modules or any rogue Google Play store apps. I was just using my phone normally and it crashed.

I popped out the battery and played around with it, trying to get it to boot up. I couldn't access recovery or even get beyond the LG logo. It would just hang there and after a few seconds, black-screen. Only popping the battery out and reinserting it would allow me to try again. I eventually left it alone until I got home, at which point I figured I'd try for download mode and reinstall the 10E KDZ via a CSE flash. It's always been a last resort, but a reliable one. I successfully performed the CSE flash of the 10E KDZ.

I thought it did the trick, as I got past the static LG logo for the first time and saw the LG boot animation, but it hung towards the end of the animation and black-screened again. Tried a few more reboots. Recovery mode still not accessible. Download mode was only accessible every third or fourth attempt. Finally got back into download mode and figured I'd try to roll back to 10D (I still had the KDZ I had previously used saved, just in case). Everything seemed to start going fine. Download mode's circle arrow animation on the phone was doing its thing, and then I hear the USB connection drop out. The arrow animation hangs, and the phone black screens. LG Tool 2014 spits out an error I can't read (the software is all question marks for me at this stage). Before it black-screened, it appeared that download mode hadn't progressed beyond 0%.

Now the phone is completely unresponsive. Popping out the battery and reinserting shows no signs of life. No USB sounds from my PC. No static LG logo. No recovery mode or download mode. Not even the lonely flash of an LED.

I've never had a phone hard brick, but I imagine this is what it tastes like.

So I'm probably out of luck, right?

I apologize for the long story. Thanks in advance for sticking around.