It's not that it was forbidden for the Titanic to have another ship following it no more than a km away, or that this sub could have had an emergency response vehicle stationed on the surface. It's just as if there was no reason to think that things might go seriously wrong. Thus, no need to allow for such a contingency. WTH?
Even today almost any ship or sub should have the option of being accompanied by an escort-vessel that could provide assistance. At the very least, there should have been the equivalent of a tow-truck sub on standby on the surface.
If even one very wealthy passenger on the Titanic paid for a ship to discreetly follow it, almost everyone could have been rescued. Instead, so many people drowned or froze to death, because it took too long for other ships to arrive.
If the wealthiest person in the-sub could have paid for an emergency response sub to be stationed on the surface, then a rescue could have been started shortly after communication was lost.
https://desertshapes.blogspot.com/search?q=Titan+Sub
https://thedigitallabyrinth.blogspot.com/search?q=Titanic+Sub