The ending of Breaking Dawn Part 2 shows that the Volturi back down without a fight, because Alice's vision makes the cost of attacking clear to Aro. Spoilers follow.
The film sets up a battle and then reveals it as a vision that Alice shows Aro. In the vision, Carlisle, Jasper and several others fall, and Bella's shield is pushed to its limit. Aro sees that the Volturi would also lose heavily, and with Alice's final witness, a half human, half vampire man, proving that Renesmee is no danger, the Volturi withdraw and leave. In my opinion, the trick is a smart way to deliver the scale of a war movie while keeping the family intact, and it could be argued that it pays off Bella's shield training in a more interesting way than a straight fight would have done. Perhaps some viewers feel cheated by it.
The Jacob and Renesmee thread is resolved in the final moments. Alice glimpses a future in which Renesmee is grown and happily together with Jacob, with Bella and Edward looking on. That vision is all the ending offers, so the honest answer to whether Jacob ends up marrying Renesmee is that the movie only promises that the two are together.
The last scene is in the meadow, where Bella drops her shield so Edward can see her memories of their life together. They affirm their love, and the story closes on the couple. There is no cliffhanger, because this is the final film of the series. Compared with Twilight (2008), in which Bella spent much of the story as a human the vampires protected, the finale gives her the strongest power in the room, and I think that shift is the real payoff of her arc. For how the films differ from the novels, see twilight books vs movies.
