Yang Kai could save any ink disciple, who hasn't ranked up using the ink, but he wantonly used every single bit of the two crystals when he was cultivating in the stream of time. It's not like he would have needed to use all of them, not leaving even crumbs behind, but that's just Yang Kai being Yang Kai. He never plans too much into the future and always relies on his main character plot armor to somehow handle things as they happen.