once a leaf has experienced some type of necrosis or chlorosis the leaf material will never regenerate. And yellow patches normally stay yellow. The leaf wont' just go back to normal when you fix the problem. The place that you should be looking to make sure you have fixed your plants is at the new growth. Some minor yellowing will turn back green but it's rare for it to happen.
If the new growth is bright green and healthy then you have fixed the problem and are on your way back to a healthy plant. Damage can be caused in an instant but the plants can take weeks to get back to "normal" so to say.
Leaves don't leech from their plants but actually it's the other way around. The buds are swelling by using up the nutrients that is stored in the leaves. As the nitrogen is sapped from the leaf it yellows, and shrivels due to the K and P being sucked out of it. Then it falls..
There is NO reason to pull anything from your plant. Unless it's absolutely necessary, and really i can't think of a time cept maybe bud rot...