In some cases there is a sheet metal cage that surrounds the hinge nuts to hold them in place, and this cage is held in with three to four spot welds. If you can drill out the spot welds to release the cage, you can remove the nuts, replace, repair, or fabricate new ones, and then reweld the cage back in place.
Looking at this marked up copy of your picture, look in the areas of the red circles for spot welds. These should be what is holding the cage in place.
