Yes there is no answer but remember if they harden the grid mean transformers than we maybe able to get back online in a year or two. If not then it may take five to ten years to replace them. Also the radiation from the nuclear power plants would kill not only 90% of the population but also make the land non-usable for 100 years or more.
So what they need to do first is harden the transformers. We will still have civil unrest, over 75% or more of the population die.