For software projects, I prefer to call them “lifelines” :-)
When someone comes with one, the first question should be "who's dead after that line ?". If no one actually dies, it's not a deadline, just a target release date.
"someone will die" is hard to act on, "XXXX amount spent on this XMas campaign will be lost and our partner X will go under" is a lot more valuable information, and potentially helps to adjust priorities too make X whole if other parts need to be sacrificed.