Is it common for the upper chest to sink in when implants are removed after 35 years? 58 years old.

Best to obtain clarification from your Operating Surgeon. Long standing implants may have created looseness of the skin once they are removed, plus all additional anatomic changes that have occurred in your body over the years, may have residual effect. I would consider possible need for a lift once the implants are removed.

Breast augmentation can oftentimes lead to changes in the breast tissue and chest wall. Over time, the pressure of the implant can lead to thinning of breast tissue and deform the rib cartilage, resulting in a depression or inward curvature of the ribs. It is more common with larger implants. 

Yes, the upper pole will be sunken in and often the skin will hang a bit afterwards.  Hard to predict for everyone. 

Since your tissue has been stretched for many years, you will have excess skin once the implants area removed. Also, the volume of the implants will be gone, and you may have some sinking in areas. Your surgeon who has seen you will be the best one to tell you what you may expect. You might want to discuss fat transfer with your surgeon to help give some volume.

The option for patients that do not implants anymore is fat grafting to fill the upper pole depression. Please see the link that shows implant removal and fat grafting.