I say relax. Just get a new valve, or wrap it in teflon tape while the beer is cold enough not to release more co2. Worse comes to worse, you just have to recarb it. If you have another keg to do a keg-to-keg transfer, I suppose you could, to try to limit the loss of co2. But you'll probably have enough of a co2 blanket to prevent oxidation it you need to replace either the lid or valve. (you just have may have to add more sugar/co2 to recarb)
I've had one beer carbed, decarb due to a transfer, recarb, freeze, decarb due to me being stupid, recarb, decarb again due to my accidental connection, and finally recarb and yet it's still pretty good.
And that was the least recarbed of my set of 3. Sad, eh?