> About "nullifying the emergency brake application when the train separates"… An automatically operated coupler will close the air lines when the uncoupling sequence is run.

Splitting a few hairs here, by FRA types will tell you that an "automatic car coupler" make a coupling automatically; all you have to do is shove the cars together (assuming at least one knuckle is open). This also applies freight car couplers and every Janney-type knuckle coupler ever made. Uncopling is not automatic, someone has to do it, either by pulling an uncoupling lever or pressing a button.

> When the train gets separated, there is no uncoupling sequence, and the air lines will not be cut

I was referring to the act of uncoupling, regardless of the reason, also closing air lines like the brake pipe automatically. "Looked good on paper", as the saying goes, and was discarded by 1890.

>(and because there are nowadays always electrical couplings as well,

As there has been since at least 1911 (that WH coupler for the IRT).

> the train management system would immediately get a "train separated" notice, and do what has
to be done.

Is the "train management system" the train crew or some computerized phantasm of an electronic engineer? The train crew has been schooled in what to do because it's their daily livelihood; that electronic engineer has learned it only in passing for a particular contract on a project.