Answer :
Yes, the end is aptly justified. The poet succeeded in teaching the readers a lesson of wisdom. By making the stupid nightingale nightingale die, he taught the readers a very important lesson. He had created this end to teach the readers that the wages of low self-esteem, poor self-belief, and gullibility can lead one to death. No doubt, the nightingale was exceptionally talented, but she was exceedingly low in experience and common sense. Hence the cunning frog exploited her; she allowed herself to be exploited. At the end, her tragic death, leaves the readers wiser against people like frogs in the society.