i think that question is not so pressing until the system is declared fully autonomous as in, no human required anymore to drive. as long as it's just an assistant, the human is supposed to brake. but, since they surely want autopilot to become an actual autopilot...

you could do the same with "normal" cameras (and probably lidar as well) i guess by pointing a laserpointer at it. the safest option is probably to just brake.

here elon musk says they don't use lidar: https://techcrunch.com/2016/09/11/tesla-autopilot-8-0-uses-r...

(as an aside, some years ago we had incidents in the news where people pointed laserpointers at aircraft pilots while landing. the pilot's appropriate response is usually to abort the landing and do a go-around, because that's the safest thing to do in this situation)