Is the questioner considered responsible for his father's death, and are expiation (kaffara) and blood money (diya) incumbent upon him, and is he deprived of inheritance, due to his negligence in monitoring his ill father's oxygen device, which led to his death?

You are not liable for anything; the default is absolution, and what you did was not the cause of your father's death. Rather, he died from his illness. Had it been a medical error, it would have been mentioned. What you feel is a result of grief, not the truth. You are not obligated by any rights or duties based on these doubts. The reference in this matter is to the doctors, and if they do not testify that the cause of death was your error, then there is nothing upon you. You are not required to investigate the cause of his death.

If there is doubt about the cause of death, there is no blood money (diyya) and no expiation (kaffarah), because the default is absolution, and financial obligations and expiations are not due except with certainty.