Try running a Linux Distro in live mode from a usb key. It will not harm your Windows install and it will allow you to access the other partition on your SD card and hopefully save your userdata folder so you can stuff it back later using the same method or with Windows over the network through LibreELEC's samba share of said folder(s). ... With a Win 10 machine you might need to find a Linux Distro that supports EUFI Booting.
Oh, this is a good idea! I actually have a laptop running Ubuntu that I keep around for stuff like this (reading/writing/copying between stuff like OSX Journal drives and NTFS, etc). Hopefully that partition isn't damaged or corrupted. So all I need to back up is a folder called userdata?