Thank you for your question. The deflated the shell of the saline implant should be removed after deflation. However if the capsule around the saline implant is thin and not tightened it need not be removed. A thick constricted calcified capsule should be removed however.
The shell or sac of a saline breast implant is made of soft rubber that was sterile at the time it was placed. It seems no more dangerous to leave an empty implant than a filled implant. That being said, the empty device is flat and has "sharper" edges and/or folds that can be irritating to patients over time. In addition, one deflated implant tends to look odd and asymmetric. The surgery to replace a deflated implant is usually much less extensive than the original surgery, as long as there are not other factors present, like capsular contracture.