I got into the same bind, and am not a very good welder so I drilled mine out. I broke off the first bit in the bolt, so then I had to get harder bits and resharpen them on the bench grinder every few minutes. Once I had chipped away the broken bit, I progressively stepped up the drills until I started to nick the threads. At that point there was so little metal left in the bolt I sorta peeled it out. It looks like your first few threads are munged up, but you should be able to chase them out when done. If you salvage the threads, use anti-seize when you replace the bolt.