I think the original point was that cancer 80+ is better than cancer at 45, so you should still try to avoid habits that make it more likely earlier, even if the chances remain 100% at sufficient time scales
I don't understand what you think this conversation is about. It's not "die quick and painless at 45 or excruciatingly painfully at 80" it's just 45 or 80. Nobody said anything about excruciating pain except you.
Do you think your dad would prefer to die exactly the same way at 45 instead? No? Great, conversation over.
What an absolutely obnoxious way to respond to someone who was willing to share his experience about a subject as personal and painful as losing his father to cancer.
I don't think it's obnoxious at all to point out that forgoing nearly half your lifespan in order to avoid a painful death implies that you don't value your life much