It would need to be very low latency if the cars can not take sufficient action fast enough to be safe. But if the cars get to a point where they are safe enough but where that safety comes at the expense of being overly cautious in some instances (refusing to drive through a sheet of water and deciding to stop) that may be acceptable. E.g. in the given example, the car only needs input to say pretty much "safe to proceed at low speed until past obstacle, then reassess".