It was a gray day on the other side of the Delaware, the sky hung low in milky furrows. Barely 12 hours after the stunning arrival of their season’s terminal phase, the Sixers gathered at their training complex on the east bank of the river and began the process of postponing what history holds to be the inevitable. Their words suggested optimism, but their tone betrayed a somber grasp of the reality that now confronts them. Staring up from a three-games-to-none hole, the Sixers’ biggest hurdle isn’t the decades of precedent that says they are dead, but the psychological baggage of knowing they were the killer.