They will blame who is exactly to blame - The Duke. Since, he is the one who voted and openly supporting executing Keira - who was actually the Saintess.
He is the one who publicly declared that Cosette - a.k.a demon Zombie to be his "real" daughter who then unleashes a demonic army onto the world. Whereas, the spirits who are pissed that the Saintess was executed refuse to help and show their anger also.
This leads to people venting their anger and house Parvis is ruined. Thats why he turns back time.
He does but only in scrambles. He recognizes "deja vu" moments.
Yes he made a deal with the mage to turn back time because the world was in chaos, house Parvis was blamed for this due to the Duke's actions by his active role in the execution of his daughter (the actual saintess) and his declaring "Cosette" (which turned out to be a demon) the "real" Parvis Princess.
This leads his house to fall into ruin and the mage was most likely compelled to help due to the catastrophe that was unleashed onto the world by the spirits being angered AND by Cosette's demonic hoarde.
I hope they continue to show the after math of her death & how the empire falls into ruin. I really want to see the looks of despair and regret once everyone realizes "oh shit, we killed the wrong one" (๑•ㅂ•)و✧