Which gate valve is stuck open? If it is one of the cockpit drains, I wouldn't worry about it. Others should be fixed but if I were you, I would enjoy the rest of the season and deal with it at fall haulout. (gee... after that advice I hope the boat doesn't sink in the slip!!) Have a tapered plug nearby in case of disaster.
To be honest I'm not 100% sure what the raison d'etra is for this particular fitting. It's on the port side in the vicinity of the u-shaped settee. I believe it's for the head, but not 100% sure. This one really looked to me like it would be very much not-good if it let go. I know the chances are ridiculously small, but I don't want to take chances that involve sinking somewhere on Lake Ontario with my family on board.
It's tempting to just handle it in the fall, but on the other hand it would really suck if my new boat sank
Might be the end of my spousal sailing approvals.