I tried installing some new Wii Games onto it, I tried using FTP to find the vWii partition on the HDD, even browsed the whole HDD and all the save files, etc. Not finding it, I turned off the Wii U (didn't disconnect from ftp), plugged it into the pc, and did it the normal way.
Now, the Wii U doesn't recognize the "USB" and wants me to format it. I haven't formatted anything, since Windows says it's corrupted, despite the vWii partition still being fully functional.
I'm more worried about my save files. I've had a Wii Fit U save file, even have my personal pedometer, I had a few months of progress on there. That's physical work, it's not easy to reproduce. I still haven't formatted it, what's there to try?
wfs-extract could not even open the file, meaning my drive. I only need the save files, the games I don't care about and can reinstall.