What causes Gregor’s death, and how does his family react to that event?

I don't think we are given particulars about Gregor's actual death. His family is relieved at his death. The family is extremely thankful for Gregor's death. Yet they also mourn his passing. At their discovery of his death, the family discovers also the conflict in their feelings concerning the insect. They felt that he needed to disappear for the good of their family, yet at the same time they loved him as their son.