I've found there's no way to predict when they'll come off or when they'll shear. I've had old rotten rusty ones come off easily and clean rust free ones shear just by looking at them.
I've done various things in the past, including laborious drilling and retapping, but last time I did mine, I just sheared them off, punched them out, and then took four pieces of 1/2 x approx. 1/8 inch mild steel flat stock, cut to about 6 inches long. I drilled and tapped holes (I've already forgotten whether I did 1/4 or 5/16, but ordinary US coarse threads in whatever size is closest to the original) near the ends of these pieces, and then inserted them behind the plate that previously held the captive nuts. They're long enough that I could just hold the ends, and minimize fiddling and fishing. A little bending to make them lie flat enough to catch threads, and I just threaded hex bolts into them. Next time, if there is a next time, I'll simply unscrew or shear them, as needed, and pull them out and replace or redrill them as needed. Think of them as nuts with their own handle.
