I don't know how good you are at drilling but I can guarantee I would have the entire cylinder destroyed before that key ever thought about coming out.

Try this instead. Mix up a tiny dab of epoxy and place it on the end of the part of the key you still have in your hand. Cut two thin strips of paper and slide them into the key slot alongside the part that's stuck in there. That will prevent the glue from bonding to the cylinder when it squishes out. Put the key handle in and hold it in place with a rubber band or a piece of wire. Let it cure for a day, then pull it out.