I can't speak to any production systems, but the ideal is to use a "sensor fusion" approach which can safely degrade or alert the driver when a sensor is lost.

I can't speak to any production systems, but the ideal is to use a "sensor fusion" approach which can safely degrade or alert the driver when a sensor is lost. Lidar, cameras, wireless communication with other vehicles and infrastructure, and with the internal sensors in the car. More concerning would be adversarially-crafted signals. (Think a Wil-E-Coyote style fake-tunnel, but for lidar and and whatnot too.)