Some of it is also due to his dad being left alone around for around 20 hours before being found, and given the timeline it probably hit just a little after the call.

I know it's not his or anyone's fault, but I think those 2 factors have him feeling like it's on him.

Some people can still walk around and function with stage 4 cancer.He might feel like that but he couildnt possibly know anything from a phone call. He shouldnt blame himself. Reassurance as someone else said is what he needs right now. My dad had a massive heart attack and was dead 45 minutes after I left him. I felt this way for a long time after but there is still nothing that could have change that or the situation.