The outcome is not easy to predict. Without treatment, some people have bouts that come and go, sometimes the disease disappears and never returns, and some people get steadily worse end eventually die form it. On average, there's about a 50% chance of living 10 years, and many people that make it 10 years still survive for a few more decades. With treatment, the cure rate is about 97%, so a different treatment approach might work this time if he changed his mind.
One thing he might consider is that when the disease is not treated, it causes about the same symptoms as radiation and chemotherapy - with radiation or chemo, the effects only last a few months, but with advanced Hodgkin's, the symptoms can persist for years.