Hi Alexandra, what is put on the death certificate is the detail of why the body stopped that day. Men do not die of prostate cancer - they die because the organs stop coping. Your dad's kidney failure may only have happened in the very last hours of his illness when he was far too ill to survive general anaesthetic or cope with the aftermath of surgery.
My father-in-law went from reasonably well to dead in just over 24 hours - a scan on the last day showed that the cancer had gone to his liver, kidneys etc without anyone realising. We knew his kidneys were struggling because he was swollen up with lymphodema but a stent doesn't solve lymphodema and the kidneys just got overwhelmed.
I hope that helps, even a tiny bit.