Long Run Nick, you are fortunate that you are still able to absorb the impact of running.
I was a collegiate decathlete and running defined me in all the sports I participated in after my competition days ended. In my early 40's I began coaching high school track and field and started to run, then train, with the athletes I was coaching. I had visions of competing at the national level in the Master's 45+ championships when I would become eligible in a couple years. The 200 meter and 110 hurdle times, that I was running with the kids, would allow for a podium placing. I began to have some chronic pain in one of my ankles and a visit to an orthopedic doctor revealed that there was no more cartilage in my ankle. I thought I could work through it but soon after I began to get sciatica pain due to over compensation so I retired from running and began my cycling passion.
Fast forward 14 years and I now train and race bicycles to get my "competition fix" and look forward to every minute on the bike. Last December I had my ankle fused with 9 screws and a plate and for the first time in a long while I'm pain free. I can even walk down a flight of stairs with something in my hands again! I anticipate beginning to do short sprints over the next couple months in preparation for the "off the bike work" in cyclo-cross racing. I have no visions of ever running any distances longer than 50 meters.
Enjoy your running while you can and do everything to enable your body to keep on running. I believe that your cycling will help in keeping your cardio up while you reduce your time running.