I believe you can get it with a hard mod, but if it's a cbhc at least or something else that's gotten corrupted, you'll need your otp to decrypt the nand to fix it. you can do that on the computer for both vwii and wii u. if you don't have your otp, I think the brick is permanent.
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if you had your nand and no otp, the system is recoverable as long as the nand is from an earlier point to where there was no corruption or cbhc install. if you have to fix the nand, you need the otp.