Concussions are technically brain damage, according to a lot of scientists. You're right that any concussion is serious shit.
This is a major one. As a Blues fan, I remember the Joe Thornton hit (which was dirty as fuck, and Thornton should've been suspended much longer than two fucking games) on David Perron. It took Perron a year to fully recover from the concussion he was given as a result of the hit - he had to be in his room in darkness for a while because the lights were too much stimuli for him.
Shanahan's concussion must be different, if not worse, given the force that the car accident must've been, especially since his head possibly wasn't in the right place for the airbags to deploy (if the leaning down to pick up his fallen phone part is true or not; who knows with the way this has been hidden from the public?).
I wouldn't be surprised if he didn't come back this year if noise, lights/stimuli, and struggling thoughts are affecting him this badly. And that's not even getting into the other injuries he suffered.
You never want something this serious to happen, even to a rival coach (especially considering that Kyle Shanahan doesn't seem like a bad person, and he's McVay's friend).