Myelofibrosis is a rare disease that leads to severe anemia. I am sorry your father is not doing well. It sounds like since the blood transfusions are not working anymore, the focus of his care has turned to keeping him comfortable.
Your question is about his prognosis. To be honest, I am not sure what his prognosis would be. My advice is for you to speak with his hematologist, as this is where you will get the best advice. If they feel he is nearing the end of his life, then I would recommend talking to the doctors about hospice care, as this would help keep your father comfortable in the time he has left.