i have always had the engine in the bucket deep enough so the cavitation plate is under water.
It had a solid water jet via the bucket before my trip to sea, and whilst out it was solid too, and engine was only run for about 10 seconds without the jet. Long enough to know if its pumping water, then when it wasnt,the engine was stopped. So im sure it wasnt run dry for long enough to do any damage. Im pretty sure i was told it took around 30seconds for the impeller to get to the point where it melts and starts to cause damage, it wasnt run for that long.
Still havent tried blowing up the nozzle end but if that doesnt work, it could be the leg. Not a problem, just a pain.