Is a physician obligated to pay blood money (Diyya) if he unintentionally caused a patient's death due to an error, given that more than 15 years have passed since the incident and the whereabouts of the patient's family are unknown?

The medical profession is a communal obligation (fard kifaya), and it is not permissible for an unqualified person to practice it. Whoever does so is liable for whatever damage they cause. If a skilled physician makes a mistake and damages an organ, they are liable for compensation, but they are not sinful, because they are an independent diligent practitioner (mujtahid). The aforementioned physician bears responsibility for compensating for their error, because damage is compensable whether done intentionally or by mistake. They are also liable for the blood money (diyah), which is not forfeited by prescription or by the patient's family's lack of knowledge.