You want pics? The timing is right because I just happened to have an open Digi Pro car on my desk. When your friend opens the cars up he will find this.
He will first have to clip the wires to the headlights loose to free the body from the chassis. Tell him to forget trying to reconnect the lights because he can't simply connect them to track power because they are LED's which can't stand the amount of voltage the track gives to the car. He would have to add more electronic parts back which I doubt he is up for if he had to ask how to disconnect the digi chip.
Next he will remove the wires from the guide. They are the red and black ones on either side of the pencil.
Now he will remove the wires going into the motor. There are a bunch of little electronics soldered between the motor case and these leads too. They are RF noise suppressors and can go too but it is not necessary to remove them.
When all of the wires are disconnect, he can remove the single screw in the center which is pointed out by the pencil. The chip can now be lifted out of the car.
He can now add new wires back in connecting the motor to the guide. None of the wires on the chip or in the car are long enough so I suggest that he use new wire available from one of the sponsors advertised on this site. Wire is pretty cheap. You may notice that this isn't an Artin chassis. It is simply one that I had at hand. It is close enough to illustrate how the wiring goes back.
If your friend is going to trash those chips please consider sending them to me. I have two Digi Pro sets and having spare parts around isn't a bad idea when you have discontinued toys. They aren't worth anything of monetary value but I will pay postage.
Mike