Article is facile and alarmist:
(1) There is not only one power grid, but three in the continental US
(2) I doubt the entire country risks being blacked out for eighteen months, though the grid might operate at reduced reliability for that time period.
(3) “Destroy nine interconnection substations and a transformer manufacturer and the entire United States grid would be down for at least 18 months, probably longer,” -- could the relevant hardware be sourced from abroad even if all possible US manufacturers were attacked?

This being said, even a month-long blackout could be disastrous for things that need power not to explode or melt down, like certain factories or nuclear power plants. A plan to keep those facilities stocked with fuel for their backup generators for at least a year shoul exist.