It's your life, buddy.
I had a galley gate valve fail on me when the under sink door closed, sending a spatula hanging on a cuphook into the wheel (which looked fine). The wheel AND stem cracked...must have been very thinned out, and I had to head to a Travelift at top speed, pumping and steering, to get lifted out. I already had the replacement on board...just hadn't got around to it. $175 for the haul and 45 minutes of concentrated pipe work and Teflon taping later, all was well, but it took some time for the undersides of the floorboards to dry out.
Anything below the waterline is not worth putting off and gate valves have no place on a boat, except perhaps as above the waterline bleeder valves. You can't tell if they are on or off, and they are cheap, dodgy things.
If you absolutely can't change it now, dive on the hull and bung in a wooden plug into the intake. I did that to change a scupper valve one year, and just after spinning on the new valve on the thru-hull, I used a rubber mallet and a
dowel to hammer out the bung (which I recovered, BTW, with a net). Even in the three seconds it took to pull out the dowel and turn off the ball valve, an impressive and intense fountain of water played over the engine compartment. Water pressure sub-surface is a powerful thing. Don't find this out the hard way.