<<Alternatively, Bran could unwittingly be the method of the White Walkers getting past the Wall, though this would be a lot less spectacular and dramatic a scene than the entire Wall collapsing, which is why I favor the horn being used in the show. Since Bran being "touched" by the Night's King in his vision allowed the White Walkers to penetrate the Children of the Forest's magical barriers, it's conceivable that Bran passing under or around the Wall on his way south back to Castle Black or Winterfell could remove the magical barrier that prevents the White Walkers from crossing it as well.>>
But Bran knows this. So why the hell would he pass through the Wall? Even if he gets trapped and dies, it's better for him alone to die than to doom the entirety of Westeros.