Hmm, you might try loosening the wheel hub, spraying some WD-40 on the axle, and using a deadblow hammer to get the wheel and hub off together as soon. Getting the wheel off the hub should be much easier at that point. If you can, use some pliers or something to press that axle key into the axle as much as possible so its sitting flat like it should.
Not so sure how usable the wheel is. If its not vibrating and the wheel itself isnt bent outside of that gouge, it might be? Hard to tell.