Cas knew the moment he helped Dean out of the "Green Room", which he still didn't understand, the room hadn't been green, he was a dead man and he didn't give a damn. Taking Dean to Chuck then sending him off to save his brother was easy, a plan. Well right now, there was no plan for him. Staying with Chuck meant holding them off, he hoped. Zachariah be damned God was still here. Cas felt him. And because of that he was not afraid to die.