I also dread the day when I have to take that decision, my dog is now 11,5 years and have had some occasions where he just faints. We have decided to wait getting a new puppy until he is gone.
Even if the loss is great, I comfort myself with the fact that he has had many good years. Always playful, just mention the word tour, and he is at the door wagging the tail in anticipation. I am sure your dog too had a good life FM.