I am so sorry to hear about your recurrence. If I were you, I would get the expander just to hold the tissue envelope if the skin on that side of your chest looks okay. If there is obvious radiation damage, then it will likely not be left when you undergo your final reconstruction. You are right that it will not add too much time to the anesthesia. The expander would not be to undergo implant based reconstruction, but instead just to hold the tissue envelope. For your final reconstruction given your history of radiation treatment, it is best to undergo autologous reconstruction. I personally do a lot of breast reconstruction in my practice. If I had breast cancer (which I do have a family history), I would undergo DIEP free flap breast reconstruction as my first choice. Since you are currently pregnant, it sounds like you will be a good candidate for this type of reconstruction. Using a latissimus flap from the back is my least favorite option. It leaves a large scar on your back and still requires an implant. The shape is never as good as the shape we achieve with a DIEP or PAP flap reconstruction. I would recommend that you look for a PS that offers free flap reconstruction. If you have any questions feel free to shoot me an email.
Recommend going with an expander as radiation was 6 years ago. If the expander fails the back flap is always an option but preserving the mastectomy flaps will at least give you an option of immediate reconstruction without sacrifice of other tissues. Best, Dr. Yegiyants