A likelihood of such an event, given that we're doing little to nothing to harden these systems, is increasing everyday.
More countries are developing the ability to carry out such an attack, plus we also are exposed to such an event from our own sun, when a massive CME sus in the future like we were hit in the past.
Matt has said that when the SHTF we won’t be just dropping back to the 1700’s (or whatever years he said)