I have twice seen a water pump shaft crawl out of its press-fit impeller; once on a Chevy smallblock, and once on a MOPAR smallblock. Check for the danger signs, like misaligned pulleys, or sudden slop in the shaft. I carved a radiator fan shroud once, when I broke a mount. THAT was interesting. I have also seen many clutch fans fail, blowing out the bearings, and consequently running the fan blades into the radiator. Was the rad carved in an even manner, or just a crescent through a few tubes? Sorry it had to happen to you, Chryco.