Strange coincidence:
Earlier this evening I was on the Exiftool homepage to download a new version. And I noticed a repair tool I had never seen before and have no use for since I don't own a Nikon camera. And then I came here and saw your thread...
You may want to try the tool here:
http://owl.phy.queensu.ca/~phil/exiftool/fix_corrupted_nef.html
Phil Harvey only writes that it repairs file from D4, D600, D800, D800E and D3200. But it is worth trying anyway, I think. If it doesn't work, contact him. He often implements changes very fast.
Your son may also want to consider if he should continue using Nikon software to download the photos from the camera. This excerpt from the above mentioned link doesn't sound very reassuring:
[Note that Nikon doesn't learn from their mistakes, and a similar problem happened 2 years ago with an older version of Nikon Transfer and the D5000 -- read here. The moral is: Don't use Nikon Transfer or any other utility that modifies the file to download your precious images!]