Alright....
My suggestions.
If there is any piece of the stud left that you can grab, save yourself the risk and drop the pan to remove the stud using either vice grips or the old 'turn the stud into a flathead screw technique.' I've found it's quite easy to turn a stud into a flathead screw by dremmeling a groove in it and taking it out with a screwdriver. Hammer and chisel method works for this as well.
Second, try an easy out. If you haven't used one before, it's not a bad idea to get someone who has to help you out. It's not a hard thing to do, however you want to make sure you've got the sizing right. Too big, you're screwed. To small, risk the chance of losing hardened steel inside the stud.
Now, it IS possible to drill hardened steel...on occasion. Using a carbide tipped bit, and the proper settings (based on bit size) you can drill out a piece of hardened steel. Problem is it's rarely ever able to be done with a hand drill.
So, take it all for what its worth. These guys pretty much said anything I could think of.