Although the surgery itself is not too common, the way the surgeon repaired the area of extrusion is common. Often when an implant extrudes the skin around that area is damaged and too thin to heal properly. Removing the damaged area back to the more healthy, viable skin and tissue will decrease the risk of a second extrusion, tissue necrosis and infections. Now, with your past history, the most important thing you can do is to follow your surgeon's postoperative instructions and go to every follow up appointment. If you have any questions or concerns, be sure to contact the office and not wait. It's far easier for your surgeon to answer questions than to repair something that should not have waited.
While uncommon, the procedure you describe can be very useful. It may also help to add coverage with an internal bra material such as Strattice or Alloderm.
Based on your description of your preoperative situation, it appears that your plastic surgeon has done the appropriate operation for you. It is not a commonly performed operation, but one that I have done several times.
Best wishes; hopefully, you will be pleased with the outcome of the procedure performed.