It might have cut through one trace, it's not that clear. But as said before: it most likely relates to the on-board audio and it looks to me like it's running to one of the rear panel connectors. Best case of the worst case scenario is if you lose anything it might be an input or output to one of those connections which could explain why you haven't noticed it if you don't use them.
I agree that screw sure looks buggered up; it could be the reason the screwdriver slipped and then nicked the board. It might be cross-threaded making removal pretty tough and creating opportunity for further damage to the board if not done really carefully.
If you zoom the image 400% using Microsoft paint, it looks more like they have scratched the protective layer off exposing and with some slight scoring of the copper rails, they struck it lucky this time, but I would definitely paint over them to help protect the copper from oxidisation or worse still shorting out.
Some advice on getting that screw out, Use some small (flat nosed not long nosed) pliers with electrical tape covering each end of the piler jaws, grip the screw head vertically and carefully twist until you can turn with fingers or if its cross threaded keep carefully using pilers until its out, its worked for me before when replacing a friends motherboard.
I'm guessing that maybe the screw is the wrong thread and was a squeeeaky fit. seen it and come across it before in the many years of building PC's at work place or for friends and friends of friends.
OR
The classic, totally wrong size philip's head screw driver heh.
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