Cannot access startup disk after failed OS install

Hello all,

While upgrading a 2012 MacBook Pro to Majove, the installation failed and now the computer is stuck at the apparently common "macOS could not be installed on your computer" message. This broken installation has taken over the laptop and I'm quickly running out of solutions.. Can not access or boot into Macintosh HD. When you turn it on it boots into the failed install message, I quit the installer and attempt to choose startup disk but nothing shows up. Holding "option" during boot only shows me "macOS Installer". I cannot boot safe mode. I've reset PRAM. There is no time machine backup to restore to. In disk utility Macintosh HD is grayed out and unmounted. I ran first aid on the drive itself, it completed fine but nothing changed. I've tried reinstalling macOS from recovery boot, it asks where I want to install it, I choose Macintosh HD, it asks for password to unlock the disk, after I enter it it "loads" for a few seconds and then the Macintosh HD drive disappears and it's back to asking where to install and only the recovery partition shows up this time. At this point I decided to just try to get into safe mode and then go from there. From googling I suspected I couldn't safe mode boot due to FireVault disk encryption. So I went about trying to disable that through terminal and it now says "conversion progress: paused" and that's where I'm at now! I consider myself a tech savvy person but as I said I'm starting to scratch my head on this one. There are no backups and there is important stuff on the computer or I would've already wiped the drive and setup as new at this point. I'll take any advice you may can offer, thanks!