I kinda find myself hoping Soo-Won will get through this illness, or at least find a way to reduce the pain symptoms and/or prolong the life time he has left, so that he may keep being the king even on the battlefield. Maybe that new herb stuff Yoon and that other doctor guy were talking about some chapters ago will serve to that purpose.
And not because i approve of Soo-Won actions or anything, his actions were always questionable and aggressive, and that recent flashback only reinforced the notion that his drive and motivation come more from personal reasons than actual care for the country. Him being the final antagonist for Yona and the bunch would be a perfect conclusion for the story.