You should definitely have a conversation with a plastic surgeon to discuss the options available to you regarding breast reconstruction.
I suspect you won’t need radiotherapy, because that is the reason you are having a completion mastectomy.
If that is the case, then you can have an immediate reconstruction with either an implant or your own tissue.
Even if you need radiotherapy, you still need to talk about your reconstruction options. My advise would be a tissue expander until you have completed your radiotherapy and then have your definitive reconstruction 6months after completion of your radiotherapy.
I hope this helps and good luck.