A mile per hour is probably about right, but that's probably per lidar. Waymo has 4 for example, so on a 300mile vehicle that could be 17 miles at 70mph.
Even if you can make it aerodynamic it's still not going to be as aerodynamic as it not being there.
Sunk cost fallacy make sense, but I'd say it's also the fear of the massive lawsuit/upgrade cost if wrong due to his statements.