Book spoilers. Since tones said it already lets just dive right into the likely outcome. If you prefer to guess your self or be surprised don't read on.
So the books have had a lot of held back content that has emerged delayed this TV season, like Kingsmoot and Brianne in the Riverlands. This leads me and many to believe another withheld character/arc will be Bran's out.
Bran, Mira and Joreen get their asses saved on their TO the cave in the books by a elk riding intellient but undead black hooded man called Coldhands. There have been theories about him being Benjen but this is unlikely in the books (I forgot this when I said s1 character TBH) - but that doesn't rule out TV merging the characters for the sake of awesome. Coldhands also helps Gilly and Sam on the way back to south of the wall after Caster's keep, showing them a secret passage through the ice at the oldest and largest keep which the Night's watch shutdown long ago...another place unexplored in the show which may become important later.