Why do nepenthes pitchers turn brown ? Actually there's a couple reasons so we'll start with the one that stops halfway. Once the plant senses that it has enough bugs in any pitcher it turns off the nectar it exudes on the peristome. It doesn't want to attract anymore insects to that particular one. So now it allows the pitcher to turn brown halfway down so it can use the energy from the insects it has caught and they are not wasted. It will continue to absorb all of the liquid until it's gone at which time the pitcher will then dry up completely and can be cut off.
Should you cut them off halfway brown or leave them ? What are you doing ?