It’s up to you how you want to play the illness in Ryslig! Yes, it will be ‘cured’ to the extent that it will no longer kill Soo Won. How you have him figure it out is at your discretion. If you want to play it out, you could choose to interpret it as a disability and start out weakened, and then it can slowly go away with his monster transformations. There’s flexibility here to do what you’d like with it.