[Chaplain]

Why not use a tool called a tap extractor? They sell them with the number of fingers to match the number of flutes of the tap. The fingers are hardened, not too hard and brittle, but more like spring steel. You clean out any chips which curl up in the flutes slide the extractor fingers into the flutes, slide the collar down to reduce flex in the fingers and use a tap wrench to remove the tap. If that doesn't work the tap will have to be burned out on an EDM machine. Don't worry about going oversize on the hole. You can always redrill it and use a thread insert or helicoil.