They all have the wolf’s blood. Bran will go nuts if something were to happen to his siblings. Looking back on the ancient story, things are playing in a somewhat similar way. The Maiden Made of Light is hidden, away on exile. This is Daenerys, the Light. The Lion Of Night, Bran the Dark one will see his siblings die from betrayals. Never mind that Jon and Arya deserved it. Bran can send minions, wights, to punish those he thinks are guilty. Let loose the wights on Westeros, like Jon set Mance and the wildlings loose against Westeros. Darkness and wights will have their day until Dany and Drogon burn them at the Trident. The melting of the northern host of ice will bring the spring thaw. The water will bring life back to the land as the ice and the darkness release their grip.