It adds slightly to the amount of "flare" in the overall scene, which will reduce the contrast index in a way that you will probably need a transmission densitomiter to measure.

Very, very carefully paint the scratch black with India Ink to keep light out of the scratch, and you'll loose just that much of the area of the lens for the imaging field.

Or say "screw it, it's worthless now" and send it to me to dispose of for you.