can not tell from picture but if there is any thing flush or above the sheet metal and you want to try to salvage it i would grind it smooth and center punch it and the drill bit will not walk. if you can not grind it smooth then try the center punch as a second plan, if that all fails you can grind it all off and reweld another nut on the under side and chase it out with a tap.or you can use a nut and bolt, you have many options at this point
