[Dodsfall]

Maybe a small sharp chisel can catch the edge of what's left of the stud and bend it out of there. There isn't much left of it.

If that fails, drilling and tapping the hole large enough for a helicoil is probably the only other alternative.

 

[Dodsfall]

I was thinking heli-coil too but isn't it to far off-center to completely drill it out?

It will depend on how much wiggle room the exhaust manifold gives you. I think it will be worth a try before scrapping the head for sure. The last alternative would be to fill the hole with a TIG welder and re-drill and re-tap.