So first of all, immediately where the cut was peformed, you will loose all sensation forever and at the beginning you will have maybe some missfeelings. For example at the beginning when I touched my scar at the hip, it felt like a needle would sting me. That occurs for every scar, your scar has no sensation at all forever.
Surgeon says that High BSSO has less chance to damage your mandible nerve than a normal BSSO. In fact your sensation will be forever diminished around the area. That is total normal and occurs in every kind of surgery what we could possible have. For example, I didn't even have a genioplasty nor a jawsurgery, just a upgraft of my lower incisors. My bottom lip lost definitive some sensation, the stimulus has to be much higher now, only then I will feel something. Younger people just cope it better than older people.