unless you're driving a Diesel. any moving car will fail with an EMP blast
spark plugs you see, they need to provide a spark for ignition on every cylinder cycle, for EACH cylinder.
diesels have no spark plugs, except "glow" plugs.
so you see, any car already NEEDS the battery running for most of it's engine duties anyway, especially more modern cars where the engine needs electronic management.
so people saying the dashboard being vulnerable to electrical failure is like ignoring the fact that mechanical failure is more likely.
think about hard drives v's SSD's: the less processes of energy conversion involved the more efficient.
imagine all the mechanical workings behind the dash to make a bunch of needles move, then compare that to a simple electronic wire connection that transmits data from the sensor directly with no coils, gears, cogs,etc
the current dashboard system is a horrendous array of mechanical and pneumatic/hydraulic systems that are far more likely to fail or give error in some way compared to a simple electronic connection to a sensor.
for the people complaining about increased failure possibility with electronic dash's, god help them when the whole drive train goes electronic and we "drive by wire".