Could a Tight Dressing After a Nipple Sparing Mastectomy Cause Decreased Blood Flow/necrosis? (photo)

Possible but unlikely. The number 1 issue would be techniques used in the sparing operation. The compromise might have been in the thinness of the N/A flaps causing decreased blood supply or venous engorging or both. 

It is nearly impossible to tell whether or not the tight dressing contributed to the necrosis of your nipple/areola, as the viability of the nipple and areola is always quite finicky after nipple sparing mastectomies, even in the hands of very experienced general and plastic surgeons. I have had patients who had partial necrosis of a nipple who were not even wrapped in a dressing after surgery, so it can definitely happen in the absence of external compression, and is a known complication of nipple sparing or skin sparing mastectomies. I am very sorry to hear this happend to you, but not all is lost, even with the removal of your expander. Give your body a little time to heal - you can still definitely have a very good reconstruction after your skin has some time to recover. 

I'm sorry to hear of your predicament and what you are going through.  Without knowing how healthy your nipples were after the procedure, any comment I make is purely speculation.  If your nipples were healthy (really healthy) and then you had the wrap put on, the wrap would certainly be implicated in your outcome.  Wraps can be done in many different ways so the technique of the wrap also matters.  If your nipples were compromised following surgery, the wrap may have still contributed to your outcome but its more likely the procedure was the cause rather than the wrap.  Nipple loss is a known risk of nipple sparing procedures or any procedure that involves moving the nipple complex.