There is a distinct type of person, very good at one thing, that is unable to understand that doesn’t translate to the rest of their life. Easiest to describe them as a high int, low wis character.

Doctors failed to communicate the situation in a way he would grasp that his choices were death or chemo. Maybe a, "that’s your choice? OK, before you go, how world you like us to handle your corpse? So you want a full autopsy to confirm the cancer diagnosis, or would you prefer we didn’t? Is there a particular burial home you have plans with? "

But in all likelihood there’s nothing anyone could have said to him to make him see reason.