Now that we have a picture, it's easy to see what happened. Orginally, there is (was) a threaded bushing that is swaged into the hole in the body. The strut mounting stud threaded into this bushing.
In your photo, it looks like the bushing is gone, as in fallen out of it's hole in the body.
The BEST fix, of course, would be to install a new bushiing. That's probably what the body shop wanted an arm and a leg to do.
An ALTERNATIVE is to find a "Riv-nut". Basically it's a special kind of overgrown "pop rivet" that, once installed, leaves a threaded hole in the center of the rivet. The threads, of course, must match the size and pitch of those on the threaded stud in your photo.
Riv-nuts can be had at most industrial supply houses who stock speciality fasteners. Unfortunately, the require specialized tools to install. Check to see if these can be rented, etc. if you go this route.
The only other way I can think of to solve this would be to cut a hole in the roof pillar from the INSIDE and fish a nut or threaded plate into the pillar where the stud attaches. That could be a challenge........
Good luck.