I have power-flushed many water pump impeller blades from these heads. Here’s a picture of a typical collection removed from one head. I have extracted these from both cracked and un-cracked heads.
To read more about the impact these dislodged pieces may have on your heads click here.
It’s hard to justify pulling the heads after a water pump failure when the engine did not overheat. But these pieces floating through my engine would worry me. Seems like something of a crap shoot.