If it is broke, you have a few options.
You can drill out the old bolt. Start with a small bit in the center, then work your way up with larger diameter bits until almost all of the bolt is gone, then you can tap the hole using the proper size tap dia and thread/in.
Could also try an "ez-out" designed to bite into whats left of the bolt and break it loose.
Get a can of PB blaster pentrating lube and soak it good, let is set a few hours and try to get it loose with a wrench, I'd stay away from the impact gun, get a 1/2 drive socket wrench and try to break it loose with the extra leverage.