He doesn't die. He's crippled and bedridden. As shown in the lastest chapter, Asher and Aria got their alibis, so after meeting the king of the neighbouring country for a while (the 2nd guy in the cover picture), they later returned home. They managed to prove Aria's innocence and punish Mielle with house arrest iirc, but later Mielle poisoned Aria's tea, which was actually a pit orchestrated by Aria, who then used that tea to kill the brother instead. Of course, Mielle was arrested but later escaped to the neighbouring country as a maid of Duchess Iris, who was on her way to meet the king for their engagement and alliance to overthrow Asher and his father. Well, it's obvious how that'll turn out xD
Oh and Aria's real father makes an appearance on the day of Duchess Isis' coup.
he better wake up soon and tell the truth because if he tries to frame this on aria its gonna be a bad day