To attempt to answer your initial question, from my limited experience, front U joints fail when the joint bearings overheat on the shafts of the joint, and “weld” themselves to the same, putting forces on the driveshaft joint bores they were never intended to bear. Once that happens, it’s like bending metal back and forth, the bending action finally causes a crack, crack causes deformation in the driveshaft joint bores, and finally the momentary out of balance creates additional distortion, ending in a catastrophic failure.
The good news, frequently, that kind of failure ends up causing a terrible car crash. You got lucky there. And, the amount of additional damage; cracked transmission housing, destroyed underbody, damaged exhaust system, et all, doesn’t seemed to have occurred.
The “replace with steel driveshaft” is great advice. Also, the tail shaft fitting. And, as already stated, carefully check the three engine/transmission mounts to ensure they are in good condition. I would also replace the rear U Joint as part of the rebuild.
