I have seen a lot of people comment that they were dissatisfied with the ending that Stephenie Meyer (SM) provided for Jacob Black. I personally think that Jacob has a very happy ending and bright future ahead of him.
He didn't get Bella, but if we are honest with ourselves, we knew that he was never going to get her anyway. I think that loving Bella would have lead to great pain and loneliness for Jacob. Here is what I mean. Human Bella would have died in 40 to 50 years. Maybe not that long considering that all of her grandparents are already dead. That entire time Jacob would have had to retain his wolf because Bella would have always needed his wolf to protect her. She is just that much of a danger magnet. This means that Bella would age, but Jacob would not. So when Bella died, Jacob would still be about 20 years old and have another 40 to 50 years to live after she was gone. That sounds kind of sad to me.
Jacob needs a very special girl to be the Rhonda to help him get Bella out of his heart, and Renesmee is just the girl for that. I know that she is a little young now, but she is every bit as lovely as Bella maybe more, she is a sweet as she can be, and she is already besotted by him. Jacob will never have to give up his wolf because Renesmee will never age beyond 17 or 20 unless she chooses to age. Unlike many of his wolf brothers, he will not be required to give up his wolf; so that, he can die with the object of his imprinting. I feel somewhat sorry for Quil who will have to wait longer for a relationship which will be much shorter or Paul, Jared, and Sam will not be able to give up their wolves in time to prevent them from out living the objects of their imprinting by a large margin. In other words, all three of them are doomed to be widowers for a quite a while. Especially Paul because he may be too hot headed to ever give up his wolf.
People who are disturbed by the fact that Renesmee is a small child, did not pay attention to the way imprinting works. Jacob has no sexual desire for Renesmee at this time. If he had, Edward would have known it, and he would have ripped his head off. The subject of imprinting upon small children was covered with Quil and Claire. As Jacob put it, Quil has about 17 years of monkatude ahead of him. But for Quil this isn't a problem because he doesn't think that way. It is the same for Jacob. He doesn't think of Renesmee that way yet. It is somewhat like when Prince Phillip was betrothed to the baby Princess Aurora. They were going to be married eventually, but he wasn't looking into her cradle with inappropriate thoughts.
I am quite confident that Jacob and Renesmee will be able to have children because I don't believe that Jacob would have imprinted upon her if that were not possible. I suspect that just like Leah, Renesmee will have a way to control how time impacts her enough to restart her cycle. My theory, and it is just theory, is that it will have something to do with her diet. I say this because it will have to be a method that she can control just like Leah can give up her wolf long enough for her cycle to restart and take it up again once the baby is born. I think that if Renesmee goes on a diet of purely human food that she will start aging again. I tend to think this because there are legends that drinking blood will slow the aging process, and these legends need some basis in fact. Also since there are legends of Incubi that can father children, these legends must also have some basis in fact. I don't believe that Joram is the basis for the European Incubi legends that there must have been European vampire/human hybrids in the very distant past. These hybrids would then be the source of the legends about blood drinking effecting aging. I could be wrong about the method, but I am sure that there will be a way.
I am picturing white wolves that would be every vampire's night mare. Renesmee is a Vampiresa or Dhampiresa. The Vampir or Dhampir were known as expert vampire hunters. Think "Bloodrayne" or "Vampire Hunter D." This leads me to believe that when fully grown Renesmee will be unusually well suited for hunting and destroying vampires. Jacob is a shape shifter the only "natural" enemy of the vampire, and it has already been demonstrated that shape shifters are unusually well suited for hunting and destroying vampires. I expect that their children will be even more unusually well suited to the task. This will come in very handy when the Volturi decide to attack again. I expect their children to appear pale and beautiful sharing specific characteristics of both Jacob and Renesmee in their human form. Even in their human form they would have very strong skin similar to Renesmee. In their wolf form, I expect white coats and the very strong skin. I strongly expect them to be the strongest wolves that the Quileute tribe has ever produced. Because of this, I would not be surprised if Leah were to imprint upon Nahuel.
He will be the next Chief of the Quileutes. Sam will give up his wolf as soon as he can; so that, he can die with Emily. This will leave Jacob as the sole Alpha and chief of the tribe. He has already proven that he can handle that roll. In fact, all of Sam's original pack will have to give up their wolves as soon as possible because they have all imprinted on adult women.
Jacob will become the next great Chief of legend because his children will be strongest wolves the Quileutes have ever produced. In fifty years, they may be telling his story around the camp fire. And instead of talking about a treaty that they made because they had no choice, they will be talking about the alliance with the Stregone Benefice that has ensured the safety of the tribe for generations to come.
He gets to keep Bella as a best friend, and adds to that Edward, Carlise, Alice, and many others as well. I suspect that even Rose will warm to him as she eventually warmed to Bella. Rose enjoys a good joke as well or better than anyone. There is no way her marriage to Emmett would be working so well if that were not true.
I was kind of shipping Jacob and Leah, but Renesmee make more sense. If Leah and Jacob would work, then why wouldn't Lean and Sam work. I think that the shape shifter gene it too strong in Leah for her to have children with another shape shifter. I think that this pack may be getting a little inbred. Jacob being with Renesmee brings new and very strong blood into the pack. For this reason, I would not at all be surprised if Leah were to imprint upon Nahuel. I also don't think that Leah could have been the Rhonda to help Jacob get Bella out of his heart. I also don't think that Jacob would have been enough to pull Sam out of Leah's heart. They both need someone very special to be happy. Jacob has found that, and I have high hopes for Leah as well. Right now Leah is happier than she has been since Sam became a shape shifter. And she will just have to get over her problems with Bella because they are going to step sisters.
All in all, I think that Jacob did very well for a minor character whose sole reason for existing was to tell Bella that Edward was a vampire.