Music was a reminder of Gregory’s humanity although it was encased in a bug’s body. Gregory still had an appreciation for music and he still enjoyed being able to hear his sister play the violin. These were all human characteristics, and in the story we are even told that Gregor wanted to send his sister to study music at college with the money he earned. So seeing these things, and seeing Gregory‘s reaction to his sister playing the violin even though he is a bug, this is all a reminder that Gregor still has human feelings and characteristics and even memories although he was a bug. Even though his appearance was shocking to those around him, Gregor leaving his room was an action that served as a reminder but he still had human feelings, tendencies, intentions, and motivations. Similarly, Gregory’s death had a human like intentionality behind it. Gregory’s family felt that his presence was a liability, Gregor himself felt a heavier weight of guilt towards the effects of his transformation. So much so, that it writes in the story “His conviction that he needed to disappear was, if anything, still firmer than his sister’s.” His death was attributed to the fatal injury induced by the apple throwing, but it was also due to this very conviction: that his presence has now become a nuisance. This can almost be described as a guilt, and it is this thought that leaves Gregory’s mind as he takes his last breath. So as we read, Gregory’s death can be attributed largely to his love and guilt for his family, which was why he “left” or died to alleviate his family.
I’m glad you mentioned music. I agree that it is one of the last remnants of Gregor’s humanness. The scene you are referring to is so interesting. He is drawn out by the music and by his love for his sister, and this contrasts, as you’ve described, with the cruelty and callousness of the conversation he overhears.