Did the same thing on the same bolt (looks like) a while back, about 4-5 years ago. Not the best spot for doing this... had to remove the PCM from above on the firewall, and the A/C accessory bracket on my 99-5.9 to get just barley enough height room for my drilll and to see what i was doing. I slightly missed center of course, and ended up using a "helicoil insert" which worked out well and did the trick.

Wonder if you couldn't drill out a small enough hole to tap in one of the square ended extractors and get that stud to spin out?

 

I would hit it with a hammer from every angle to loosen it up. Then I'd use a very sharp chisel and drive it into the side of the bolt but off-centre to the right a bit. Use the chisel to slowly back out the bolt a bit and then try using vice grips again. This is where expensive vice grips pay off. They won't deflect as much and usually have more aggressive jaws up front.

You could also have a welder weld a nut onto the bolt. Just place the nut over the end and weld up the centre.

Steve