Known outcome. Neck contouring may involve initial use of a fat melting (lipolysis) laser and/or surgical separation of the skin in this area from the underlying structures. The heat from the laser or from instruments used to stop bleeding under the skin may shock or permanently injure some of the hair follicles resulting in a small bare patch of skin.
Laser may. Have damage hair follice roots so they wont grown any more.
Cicatricial alopecia. This is called cicadricial alopeciathis or hair shock due to follicular injury or trauma induced by the surgery. This can cause hairs to enter the telogen or sleep phase for an average of 6 mos. Minoxidil or Latisse (bimatoprost) (off label use) may help but give it time first.
Follicular trauma. Most likely the general trauma in the area has induced a resting state in some of the hair follicles. This should revert to normal as the tissues recover, but will probably take several months.