Can you try drilling the stud with progressively larger bits?
Maybe tight quarters, but if you can, you could get the stud thin-walled enough to extract it, or re-tap the hole and get the remaining stud pieces out.
So I can only say what I would do if I needed to get that bolt out. I made this jig to helicoil the stud holes. Its just a matter of making the bushings with the desired holes for me now. I would use a long center drill to catch the center of the hole (with appropriately sized hole in a bushing for the center drill) and then use a drill one size under the tap drill size to drill it out. Then I would try to break the remaining material by digging it out, and worst case go to tap drill size, drill and re-tap. Absolutely worst case helicoil - might be doing that anyway.