As to how one can assume failure of a 'water deluge"... Do they have one? Where are the water towers? Not visble anyway. Isn't that why the stack is fired off a raised platform? And by what physics could debris possibly manage to return into an engine against that phasmagorical maelstrom of thrust? It's not as if it's an atmospheric engine breathing ambient air full of debris is it? Any debris from spalling concrete (which one would imagine the dimmest of SpaceX engineers would have thought of...) would simply be blown into the next county.
Sorry, just no.