21hp V-Twin mower.
NICE! That'll throw the dog toys when they get run over!
Those pumps are on LOTS a stuff. Outboard boat motors, go carts, mopeds, you name it. Not uncommon for the diaphragm to fail in them either. Often when they do the gas from the tank will drain down into the motor and hydraulically lock it. Makes it VERY hard or even impossible to turn over. Coulda been what killed the battery when the starter motor couldn't turn. Nothing you could have done to prevent it though.
Check the oil in the motor. If gas did drain down into the cylinder it could have been forced past the rings and into the crank case. If it were me, I'd just change it to be safe.