First of all, if sensation is intact after surgery it remains intact long term. You may even go through hypersensitivity as everything heals, but your nerves must be intact to provide any sensation. If intact after surgery, they remain so.
If the nerve or nerves (one or both sides) are bruised, stretched, or partially injured, you could have numbness initially but recover sensation once the nerve(s) heal. The longer nipple sensation is absent, the more likely it is permanent. So, you HAVE dodged that particular bullet! Permanent numbness occurs in about 15% of patients who undergo breast lift procedures, and in 5-10% of women who have implants only.
As far as necrosis (dead skin or nipple from inadequate circulation) goes, if the tissues are alive after surgery, the only way they die is in response to decreased circulation, which CAN occur if you have post-op bleeding, infection, or even excessive swelling that constricts blood flow in the skin flaps before they have fully healed.
The easiest way to cause necrosis, however, even after surgery, is to resume smoking, use of ANY nicotine product (gum, patch, spray, inhaler, etc.), OR exposure to second-hand smoke. Nicotine is such a potent vasoconstrictor that you could have adequate circulation after surgery, get a false sense of security, and CAUSE dead tissue by resuming smoking.
YES, even ONE!
Perhaps I'm wrong, but your signature "CantWait77" seems to indicate you may be craving tobacco. Until you have healed completely and have your surgeon's clearance, smoking is the easiest way to cause yourself problems you really don't want. Trust me on this, I have had a patient or two that have done this and then when the skin is dead and we're doing dressing changes and talking about skin grafts, they invariably say "If you had only told me it would be this BAD, I wouldn't have started smoking again!"
Sure, I really believe that.
It WILL be THAT BAD!!! But I keep trying to tell this to patients. Here you go again. Good luck and best wishes!