My wife has had a number of NEF files become corrupt and it appears there is no way to fix them. I have, however, been able to remove the jpg from the file to give her some hope of having access to the image. The issue is that she has about two hundred of these and that will take quite a while.
I'm not very good at this stuff. I started with the cmd line exiftool -b -JpgFromRaw SAMPLE.NEF > sample.jpg and it worked fine. I batched it to look like exiftool -b -JpgFromRaw -w _SAMPLE.JPG -ext NEF -r. But it isn't doing anything. Any help would be greatly appreciated.
Try this:
exiftool -b -JpgFromRaw -w %d%f_%ue.jpg -r -ext NEF "F:\Your path\to\Directory containing files"
The -w option expects a format string (%d%f_%ue.jpg, in the example).
There is lots of information in the documentation about format strings.
The -r option causes processing of files in all sub-directories. Specify a directory on the command line, not a file name.