[Christ]

Yeah, whatever you do, you'll need to grind/file it.

Or, you could try to JB-weld another screw to it, that might work too, but not likely.

I personally suggest flat file, then center punch, then small forward drill, then extractor.

If it's large enough, you could also try filing a slot into it with a cut-off wheel, then using a screwdriver. However, if it's in there tight enough that it broke off, a screwdriver will probably just strip the new slot out.