My take on the situation you have. If I had a plant in that situation, and felt I needed to do something quick to save it, I'd chose one plan of attack and go for it. Could either save it or kill it and it sounds as if it's on it's way out anyway so what do you have to lose? Actually have something to gain possibly if what you try works. And if it doesn't possibly learn also that what you did didn't help so if it happens again (lets hope not) you can possibly rule it out as something to do.

Here's another thought. Transplant it into a 5 gallon bucket. The container it's in right now looks sort of small. Heck maybe it's root bound to the max! Might be why it's not getting any N. And if you thought it might be N deficient I'd spray down the new soil with some blood meal tea so it has some N readily available as soon as possible.

Just some thoughts. Good luck!