I believe numbness or lack thereof will rely on three things- the skill of your surgeon, technique, and the equipment they use.
Often we fear nerves being severed/cut, but even simple manipulation such as stretching the nerve can harm it.
Getting a genio WITH lower jaw dramatically increases the risk.
For technique, people who have IVRO are less likely to have damage compared to BSSO.
The other is equipment, I have heard of surgeons using piezoelectric devices to minimize nerve trauma.
Piezoelectric device or piezosurgery device was originally developed for the atraumatic cutting of bone by way of ultrasonic vibrations and as an alternative to the mechanical and electrical instruments that are used in conventional oral surgery.