His father had gone lenient on him, all things considered. Cassian would be stripped of his title as Crown Prince and sent to the border to fight. It was a punishment, but also a calculated move—the Emperor recognised the value of Cassian's powers and wasn't willing to cast him aside completely.
Cassian's mother, the Empress, had been both relieved and terrified by the news. She was glad that he would live, but the thought of him seeking vengeance against her loomed in the back of her mind.
She remembered everything she had done to awaken his powers: the brutal physical and mental torture, the relentless manipulation, all in the name of securing her position as Empress.