you have to try to drill it out or use your extractor. if the extractor can get it out then great! But if you have to drill it out, you may risk ruining the threads. so center punch the bolt, then drill with a small drill bit like a 5mm or sumthin and then use an 8mm or 5/16 and you should be able to get the rest out or it should jsut tear out by itself be sure to clean up the threads using a tap.
worse case scenario you need to use an insert thread, and that will get costly if its done right.