Age 70, Mentor, round, saline, under muscle - when is revision/replacement necessary?

I am a 70 yr old woman who had breast augmentation in 2020. Mentor round saline under the muscle a replacement of saline that had been placed over the muscle approximately 10 yrs prior. When placed under the muscle, the size was larger, 475cc, and while they always looked natural, were also large for my small torso. Now, 20 yrs later, a combination of implant age and approximate 6lb weight loss they are smaller. Actually just right for my body, but now I worry about longevity of implant.