Door pin issue

If you want to try another method that doesn't require a welder, here goes..
On the inside of the pillar there is a sheet metal box which traps the nut in that general location. To bend the top of that box open allows removing the nut. Now cut a piece of metal (16 gauge or better) to the size of the box and slide it in there. 4 small pop rivets placed at outer corners reinforce the sheet metal and still allow the nut to go in. Then the oversized washer on the outside helps too.
Any attempt at repair is a waste of time unless you correct the root cause.
Rebuild the door hindges first then repair striker and set it positioning.