If the bolt broke because it was overtightened then with the head off there is no longer any tension in the bolt and it will come off easy. If the bolt is cross threaded or seized you will be replacing the crank. I used to see this all the time on early h23 motors and could never extract the bolt. If it siezed then you can remove the crank and have a machine shop redrill and tap the block but at that point you might as well replace the crank.