If you are asking how long do the implants last, then the answer is unknown. Nursing, mammograms and breast exams are all still posiible after breast augmentation. There is no causal link between silicone gel implants and autoimmune diseases in today's literature. Capsular contracture is a variable response to implants and multifactorial. Good surgical technique and massage avoid encapsulation.
Liposuction permanently removes the fat cells.
They do not return. This is not to say that you now have a blank check to eat, but rather that with a healthy diet and exercise, you should not see a return in this area. Your propensity to store fat in the area remains unchanged and the remaining cell may pick up the work and store fat there if you eat too much. I have performed this operation hundreds of times on thin women like your wife. With good judgement and the proper implant selection, she should look fabulous.