Curiousity here. I have had reconstruction after bilateral mastectomies, with a lat flap on one side--that means fat was added to pad things.

After my surgery, will I lose this fat padding like everywhere else, or does it behave differently?

You can will likely lose some of it. I didn't have breast reconstruction, but I did have breast implants and fat grafting to my buttocks before I had gastric sleeve surgery. I eventually lost all the grafted fat from my butt. And I have lost most of the real tissue around my breast implants (didn't have much tissue to work with in the first place) to where i can now feel/see the implants themselves through the skin in certain areas.