Post mastectomy op - possible necrosis nipple which seemingly continues to fight - is this normal? (photo)

It can play out several ways.  If you have sensation that is a very positive sign.  the nipple itself may slough the top layer of skin but then heal.  Repost pictures to let us know how you are doing.

It may be hard to tell from the photos as this does look like early necrosis... venous engorgement is one possible explanation for a living yet darkly colored nipple. If the tissue is left alone and is dead, it usually hardens and dries up as time goes on, forming a thick black scab. If dead tissue has moisture/ointments/active wound care, then the dead tissue melts away and leaves raw tissue (or whatever is underneath) visible. If it is alive, it should continue to heal and improve. If it is dead, your doctor will help with removing what needs to come away and work with what is left behind. Good luck!