I must admit that I have a pretty high degree of confidence that if the director of NASA briefs the president that this is happening (which he will know with a very high degree of certainty), such a shutdown would be effected - and similar for pretty much every other civilized country on the planet.
Any deaths that would happen from shutting down the power grid would happen anyway, but this would allow for mitigation strategies to be put into place. Hospitals already have emergency generators, so it not like they're strangers to the concept. Also, the 2003 northeastern blackout affected 55 million persons for up to two days and only ten fatalities were attributed to the outage.
Anyway, this seems like a good thing to have a contingency plan written up for. The NASA article suggest there isn't, but that just might be that they don't know about it - they wouldn't be responsible for executing it anyway.
It seems much more likely that the grids around critical infrastructure would be taken offline, but major metropolitan areas would be left connected. In a TEOWAWKI scenario, we would expect a government to prioritize its military capacity ahead of the comfort of the civilian population. Also, the riot and crime risk would heavily weigh against any actions to take cities offline, not to mention the PR nightmare of being wrong.
It seems "the grid" is a singular thing here. Either you shut it down completely (and then back on later), or you lose it completely.
If you leave cities connected, and the solar solar storm hits, then the cities are without power for a much longer period of time than if you took preemptive measures - with all the risks of crime that follow. Also, I'll refer to the 2003 blackout for a dry run of the mayhem that will unfold in the face of a vast power outage (ie. not much), and in this case, you'll even be able to provide a quite fair number of hours warning, so most people should be able to get home - you won't have a million office workers stranded in Manhattan. Hoarding will happen, though, and it won't be pretty. That survivalist nutcase guy at the end of the street will have a field day when he struts out of his well-stocked bunker after the power comes back on.
The PR nightmare of having shut down the grid for a few hours with warning (presumably, you'll shut it down immediately before the hit is expected, so if you're wrong, you can turn it back on fairly quickly[1]) is much, much lighter than frying the entire nations electrical grid, causing trouble for years because you acted against advice from your NASA director. Also, if he was wrong, the NASA director will make a pretty good fall guy and it won't even be all that unfair. If your PR guy can't spin "I listened to the best scientists in the country and followed their recommendations, I'm sorry they were wrong, but better safe than sorry", fire him too.
1: Spinning a grid back up isn't anywhere near instant, I know, but it'll be a lot faster than having to rebuild the grid first.
Not true. You can turn off the power in a nuclear plant pretty much instantly. You can turn it on pretty much instantly. What you can't do is efficiently turn it on and off - it takes time for the reactor pile to warm up after you've dropped the control rods to shutdown.
But there's no specific reason you need to do that - the reactor won't be effected, the control rod circuits are heavily shielded and fail safe these days (i.e. if power does go, the arms holding the rods drop them in automatically when the electromagnets fail).
For a day or 2 of shutdown, you could leave the reactor hot.
Sorry but you're simply wrong here about the conditions of the shutdown. These are not planned months ahead shutdowns they are near instantaneous emergency shutdowns and it takes a while to recover from those. After the 2003 blackouts the nuclear plants took the longest to be brought back on-line.
This isn't a reactor SCRAM though - or at least, it doesn't have to be. It's a momentary need to disconnect the reactor generators from the electrical grid.
If you planned in advance (to manage the reactor's thermal state - i.e. keep the heat exchangers going) in such a situation, then all you're doing is disconnecting the transformers.
The problem is no one's planned ahead for this type of shutdown of a nuclear plant. The procedure you follow is the one you have since you definitely don't want to make it up on the fly with a nuclear plant.
That would feel like the apocalypse if it happened. It could certainly be done in time, but doubt you could convince people it was real.
There would be a ton of deaths, so it's not something to do lightly.