I had a similar situation this year when my father was diagnosed with prostate cancer. It's quite advanced and although he is undergoing treatment it is not a matter of if but when. This is complicated by the fact that my parents emigrated many years ago!
I made a decision to not dwell on the negatives of the situation but rather, try and create as many positive situations as I could. I call a lot more than I did, I visit more and I try and take much more of an interest in his life, not just in the medical details!
My Mum calls it building memories but I have taken him to a couple of events he really wanted to go to and I watch sports he is interested in to give us more in common! I am actually really enjoying the sports and it's great to connect with him in a different way to previously!
I would never dream of telling you what you should do but I've found this has really helped me deal with the situation and come to terms with it. I hope my father has enjoyed our bonding as much as I have.