Nobody said it would switch off and never come back on. The damage over the grid wouldn't be little onsie-twosie parts broken like in a typcial regional power outage. It would be widely distributed component failures that woudl cause massive cascading failures.
Perhaps you are too young to remember in 2003 when a rather simple failure caused a massive, prolonged power outage in northeastern US. So imagine is the *entire* electrical grid had component failures are random locations. Add on to that the fact that the communications systems would completely go down, and getting power back up and running wouldn't be as simple as you think.
Obviously people would have generators, old cars would still work etc. And after a week, when people started to riot and civil disorder stepped up, you'd might lose your generator or your life depending on your ability to defend yourself.
But again...diesel generator. May or May NOT work, depending on what electronics are built into the device to run it. Modern diesel automobiles run off an electronic ECU (engine control unit). I'm not certain what you think is so special about "diesel". Old gasoline generators will also run, if they are not controlled by electronics.
My parents have a generator wired into their home...and it's has a very fancy electronic control panel...and wouldn't work after those electronics got fried.
I'm certain you are a very smart Electrical engineer, abge - in fact, I know you are - but you are also somewhat naive at times. Sorry, not all diesel generators would work. And when you fuel supply runs out, they certainly won't work. and when civil disorder is the rule of the day, because the grocery stores are empty, and because people just generally suck and segments of society have a nasty habit to riot and steal and commit acts of violence when they think they can get away with it -- it could be an extremely devastating scenario, regardless of whether or not your diesel generator may or may not work.