Just overexpose the shot, using levels and see if you can get any detail in there. The thing is, the most detail is in the midrange of a shot, with less detail in the highlights and shadows. Generally. So if you bring up a shadow area like that face, you’ll probably get a flat gray blob with a little bright mouth.
If detail wasn’t recorded in the first place, you can’t invent it. Unless you’re an illustrator, and draw a new face in there.
Your friend should fire the DP.