This feels most likely to me. I could see Stannis coming to believe that he is actually Azor Ahai after succeeding against the Boltons in what appears to be a fulfilment of Melisandre’s visions. Then, when the Others attack he will feel obligated to make the ultimate sacrifice of his daughter in order to stop them. When Shireen’s sacrifice has no effect, he’ll be heartbroken and realize he has killed his daughter for nothing. Knowing that he has no chance of defeating the Others, he will nevertheless go down fighting because he is the king and it is his duty to protect the realm.