Lucius was dying, Draco knew that before arriving at Azkaban. Something related to the blood curse– as Severus had explained to him earlier that term– was killing Lucius. He had been... separated... from Narcissa. From what Draco understood during his own research, the bond that was required to stabilize the blood curse through a soul bond was absolute and the distance between his mother and father was ultimately what caused his demise. 