I do have a fix for a boot failure on a Windows 10 system, and this repair is based on a system that was upgraded from Windows 7 to Windows 10.
As you have no doubt found out, there are a plethora of fixes for Inaccessible Boot Drive, boot problems, updates, etc. for Windows 10. I finally found a solution after being asked to look at a non-booting system that had been hacked.
The symptom was that a known good system was now booting with an error, restarting, then stating to run diagnostics, or run startup repair, or inaccessible boot device, and so on. I used the Command Prompt to perform a number of repair or diagnostic steps including CHKDSK, BOOTREC, SFC, and others all with no errors. But also still failing to boot. The BIOS was played with resulting in no improvement.
1. The user data was copied using Command Prompt COPY command from the failing hard disk to a USB drive.
2. Once the data was copied, I formatted the full drive after using DISKPART (using Command Prompt) to remove all partitions.
3. My analysis was telling me the hardware was all OK, I could boot UBUNTU and other UNIX-based utilities with no problem. I was in a perpetual circle of restart Hell, wasting a lot of time watching Windows 10's dots circling the blue background over and over. The disk was clean, functioning, but would not boot into WIndows 10.
4. I decided to create an ISO DVD for Windows 7, since this was the first OS before upgrading to Windows 10. I used this site https://www.pcsteps.com/45-download-windows-7-iso-legally-free-digital-river/ to download the Windows 7 image, and then create the ISO disk. NOTE: This will load Windows 7 on any system, but to activate the system, you need the System Key which is on a sticker on ALL desktops and laptops...if it hasn't been yanked.
5. Change the boot device to the DVD or USB, whichever has the Windows 7 image, and restart. The process will install Windows 7. This took more than an hour on the system because it downloaded all updates for Windows 7!
6. Once the system has been configured and restarted, I loaded a few programs like Google, Malwarebytes, etc. and ran them, restarted the system, ran more programs, and restarted. No problem.
NOTE 1: I am going to assume at this point that Windows 7 starts because the hardware drivers were reloaded correctly from the original Windows 7 level.
NOTE 2: As mentioned earlier, to activate this version of Windows 7, you will be asked to provide the System Key.
7. I then installed Windows 10 as an upgrade of Windows 7. The Microsoft page to create the ISO disk is here:
https://www.microsoft.com/en-us/software-download/windows10 or here for Windows 10 PRO: http://www.redmondpie.com/download-windows-10-pro-iso-file-without-product-key-from-microsoft/ . The System Key will be needed to activate these versions of Windows 10.
8. The installation will create the appropriate partitions, etc. and will restart. This takes some time, and you should then install all updates. Go to Cortana and say or type System Updates.
My impression is that the existing hardware drivers were originally configured for Windows 7, and to install the right drivers to the right hardware during the Windows 10 install was, to me, a guessing game.
Microsoft update/upgrade/installation processes and procedures are meant to start with minimal input from the user. They work as long as you let them finish. When they don't work, I would say Keep It Simple and consider reverting to the original OS, then upgrade.