Kai had come up with his plan in a hurry and under serious pressure, but it had worked. Adam wasn't cruel enough to let Kai kill himself, given the circumstances.
Moreover, Kai's last words awakened something inside Adam. He realized that those words came from the depths of Kai's soul.
Every being wanted to live, especially those who had already accepted their imminent death from poverty and disease, but suddenly had the opportunity to climb out of this abyss, once and for all.
The reason was very simple - if Kai became a Phantom, his disease would simply disappear. The genes of the Phantoms were strong enough that their immunity could cope with all the diseases that were fatal to ordinary people.
However, it was worth realizing that there were no incurable diseases. For a certain amount of money, one could cure any disease in the Citadel, all it took was money, that's it.
