Several years ago, there was a study done on exactly this sort of event. It concluded that the power grid was in severe danger from it. Those lines stretch for many miles “uninterupted”. It concluded that the most vulnerable part were the huge transformers at either end, which were likely to be destroyed, and which would put out power for about 70% of the population.
I remember something similar to that, after the last big power out due to a minor problem with the grid that began in Canada. I never liked how seemingly fragile our power grid is, especially in light of possible terrorism. But it’s hard to know how serious the problem is hearing almost nothing about it.