OK, so this option is obviously the worst case scenario for Jon and Daenerys's child, but hear us out. What if the "Prince That Was Promised" actually was promised . . . to the Night King, as an offering to end the war between the living and the dead? Because of the horrific secret revealed at Crastor's Keep during season two, we know that the White Walkers readily accept newborn boys as offerings beyond the Wall. A true-born heir to the Iron Throne would make an especially good offering, and might be enough to appease the Night King.