If it's a paper one, there hasn't been a fee for anyone recently as far as I can tell. Call 'em up, they'll probably tell you to write VOID on it and scan it to them in an email along w/ a short note saying that you don't have use for it anymore.

If it's electronic then presumably it has been attached to a reservation? If it's attached to your reservation and you're an EXP, I imagine you might get traction calling to return without a fee. Not sure there are data points since the changeover to electronic. Maybe they'll base it on the account owner like with miles, but maybe not.