What makes you think there were no survivors? Have you read Tacitus? Tacitus mentions survivors who had fled the battle pointing out sites of the action to Germanicus when he marched to the site some years later. Plus there were prisoners, many of whom were sacrificed. To say nothing of the Germans who survived. Of these Segestes was taken by Germanicus to Rome, Arminius murdered by his people, and plenty of others involved in the attack maintained relationships of various kinds with the Romans