With an EMP, electronics get fried when they are on or off. At least that is how I understand it.
“the grid” is only damaged - generators and such - if they are on, not when they are off and their lines are dead.
If they are not “live” the EMP affect has no “electromagnetic” activity to disrupt in a damaging way. It’s the same as “do you need a surge protector if your circuit is off/dead”? No. Any “electromagnetic pulse” will not get passed/into the off/dead circuit.
I think our NatSec planners understand the EMP attack potential and when and if necessary have some options planned.