As far as quality of life after TX, the advice your father is being given sounds right to me. My personal experience is that the surgery has had the most negative impact on my life.
At any age the radiation is tough enough that for many of us the chemotherapy side effects are somewhat obscured. Stage IV requires aggressive TX. Your father is of an age that he will remember: "In for a nickel, in for a dime" with the radiation alone being the nickel and the added chemo the dime.
You sound like a wonderful daughter
charm