I sure hope you have nothing to worry about.

I would say as long as they are not in pain let them live out their lives. If they pass away at home in their sleep well that's wonderful, I bet the dog couldn't have been happier. If there is any decline in her quality of life or if she starts experiencing any pain then that would be the time to think about letting her go peacefully.

Hopefully you won't have to make this decision for a long long time.