If anything went wrong, they were held responsible:
Cashel Man suffered violent injuries to his back and a sword or axe wound on his arm, but this level of violence is not unusual for bog bodies. Keeper of Irish Antiquities, Eamonn Kelly, who has worked on all the major bog body finds, theorizes that the bog bodies died violent deaths as a form of sacrifice.
He explained to the BBC, “When an Irish king is inaugurated, he is inaugurated in a wedding to the goddess of the land. It is his role to ensure through his marriage to the goddess that the cattle will be protected from plague and the people will be protected from disease.”
He continues, “If these calamities should occur, the king will be held personally responsible. He will be replaced, he will pay the price, he will be sacrificed.”
(H/T: Celtic Myth Podshow)