The interconnecting substations are HUGE. Not to say thy can't be harmed, but it would be damn tough to take out 100% of their interconnecting function.
And even if the interconnecting function is removed, the separate grids will be able to take and distribute power, again, within capacity constraints.
It's always amazing to me for guys like this writer to not understand the grid. While the assets of the electric power grid are in need of upgrades, the grid is truly one of the most incredible engineering feats in the history of man. While some point to the blackout in the Northeast, they fail to point out that an operator saw what was happening and hit the 'disconnect' switch stopping the cascade or that, if the switch hadn't been thrown the interconnects may have caused it to continue to roll, but, many of the legs of the grid could have recovered quickly.
Granted, trying to understand ISO's, RTO's and the various aspects of the electric power industry is tough, if one is going to write about it, I would hope they would read and learn about it first.
And, I am NOT saying, by any stretch, the grid is immune from hackers, sabotage or terrorist activities. But, does anyone know where they get their power from?