[Colorado Doug]

If there is enough stud remaining, screw two new nuts onto the stud. Hold the bottom one with a wrench while you tighten the top one against the bottom one. Once tightened, use a wrench to loosen the bottom one. This will remove the STUD, complete with the stripped nut and all. replace the stud and nut when you put the pan back on and you will be good as new.

[Yardstick]

I agree with this. The nut is a lost cause. Remove the stud instead. Then put in a new stud (and nut).