When it gets to a point where you see your nodes hanging down. Then it'll most likely be a goner if not a sure thing.
Some leafs might of started to eat the N in other leafs. It just tried sucking your plant dry.
Their is a journal on here about crop steering by holding back feeds. But, u need to get to it before it gets to that. The bounce back is always quick. If it does get to this point again. Don't feed with nutrient feed of any sort. Just water
Good Growing