Too little too late is the name of the game for our dear Spider, but at least he goes out doing what needs to be done. He sees that Daenerys's rage and ambition have culminated into ruthlessness that cannot be stopped and he sends out letters proclaiming Jon as the true heir to the Iron Throne. Regardless of his fiery end, his last act as protector of the realm is to ensure that Daenerys can never been seen as the rightful queen of the Seven Kingdoms. So at least, metaphorically, he goes down swinging.