DIC represents an end stage of severe septcis which may be the result of other clinical problems and other forms of system failure. AT3 would not be a "cure." If AT 3 signifantly improves survival in a condition that is fatal in about half the cases, it would be embraced by the medical community. Septcis and DIC can occur in young healthy people sometimes from fairly innocuous factors eg. using tampons.
I do not know whether the subset was biased toward "surviors". My impression is it was not. Dew may know more about this. I think its a good question.