Default Dead end

First - my device (Alcatel One Touch Idol Mini | Alcatel 6012X | Chipset: MT6572) doesn't have a forum, so that's why I'm posting here.

I tried to install XPosed via the app and failed miserably - the device is currently in boot loop. Now I need to restore my old /system/bin/app_process file (which, luckily, is backed up). I don't have custom recovery and haven't granted adb superuser permissions, my boot loader is locked and Alcatel obviously doesn't provide a way to restore the original firmware. The SP Flash Tool simply "searches" and does nothing.

The short version is, I need to remount /system as rw and see absolutely no way to do it.

Are there any suggestions on how to obtain root from adb or restore the original firmware?