Hydrogen vs. Battery Electric Cars

If we replaced all 5 million cars in California with hydrogen fuel cell cars, it would fail - there would be months- long lines to refuel at the 47 hydrogen stations. That shows just how absurd your "If everyone went BEV the grid would crash" argument. 
Because of course it won't be an overnight transition, it will take over a decade before a majority of cars on the road are BEVs, giving us time to upgrade the grid to handle the load. But upgrading the hydrogen refueling capabilities to handle a majority of cars would be far more costly than upgrading the grid. 
It's a moot point, considering that fuel cells are expensive, hydrogen storage is expensive, and most of all, hydrogen fuel is a lot more expensive than electricity, and always will be. HFC cars simply are not economically competitive to BEVs, the only place hydrogen fuel will be used is where the weight advantage of hydrogen overrides that much higher fuel cost.