I'll second the thought that this shouldn't happen, for three reasons.
First, the seacock SHOULD have 3 bolts (or lag screws) through a flange and into the hull, making it impossible to turn.
Second, the through hull has straight threads, and so does not achieve an ever-tightening condition as tapered pipe threads do.
And third, I would be VERY skeptical about the ability of the through-hull to actually reach the ball. I would expect a very distinct "end" to the threads, before the ball is reached.
Oh, a "short haul" may not be as easy as it sounds. My new-to-me boat needed a new centerboard cable, a fairly easy job but one which cannot be done on the hard. The yard would not let me on the boat when in the slings, so I had to pay them for the work (quoted $500, billed $1000).
And finally, seacocks CAN be replaced in the water. You can dive the through hull, and either put in a rubber lever operated cork, or put a small plunger over it. I've never done either, but I know people who have. I have replaced a shaft seal
in the water, and while a LOT of water comes in, a good bilge pump
running and a reasonably quick job (deliberate, NOT rushed) kept the water well below the floorboards. It does take a certain degree of nerve.
'79 Sabre 34