My view is not to end when on top. As long as there's a chance to win big races, maybe even another GT, there is still reason to continue. Losing some battles in the end of your career is in no way a stain on your legacy.
Look at Ole Einar Björndalen. Could have retired many many years ago, and was since about 2009 not as great as earlier. He would win gold medals but only through being part of a dominant Norwegian relay team. In 2014 however he won another individual gold medal in Sochi, an insane feat. In the World Championships this year in Oslo he racked up two silver medals and a bronze. Not as good as he once was, but still good enough to win races. Now he's continuing until the 2018 Olympics, and will compete at the tender age of 44.... (not really revelant that he's not the most likable guy ever, he is undoubtedly the GOAT)
Look at Ole Einar Björndalen. Could have retired many many years ago, and was since about 2009 not as great as earlier. He would win gold medals but only through being part of a dominant Norwegian relay team. In 2014 however he won another individual gold medal in Sochi, an insane feat. In the World Championships this year in Oslo he racked up two silver medals and a bronze. Not as good as he once was, but still good enough to win races. Now he's continuing until the 2018 Olympics, and will compete at the tender age of 44.... (not really revelant that he's not the most likable guy ever, he is undoubtedly the GOAT)