I always use a Craftsman impact driver to take out those screws if they are even remotely stuck. Because of the soft metal. I have another cheap asian impact driver that does not work as well. Just a firm twist and a tap of the hammer does it for me every time. If it is completely stripped out, drill out the head and pull the rotor. Then soak with PB Blaster or your favorite liquid wrench and try the vice grips. Or cut a slot in it after the rotor is out and try again.