Dominic Toretto's son, Brian, is the reason the strange picture for the Fast and Furious franchise.
Dom Toretto remains the central character in the Fast and Furious franchise and his son, Brian, is now an important part of the story as well. Brian is Dom's son with Elena Neves, whom Dom had a relationship with while he thought his true love, Letty Ortiz, was dead. Dom finds out several years later, during The Fate of the Furious, that Elena had gotten pregnant while they were together and that he now has a son. He names the boy Brian after Elena tells him she had only given him a middle name up to that point. He is named Brian after Dom's brother-in-law Brian O'Connor.
The Fast & Furious Movies Don't Need To Kill Another Parent
The reason Dom Toretto is safe until the end of the franchise is that he is now a father, and the Fast and Furious movies don't need to kill off another important parent. The series revolves around the importance of family after all, and Little Brian has already lost his mother at this point. It would be cruel and contrary to the franchise's central theme to kill Dom as well. Moreover, Dom lost his own father as a child, marking another moment in the franchise that saw the death of an important parent.
Killing Dom when he has a young son that needs him would simply be departing too far from what the franchise is all about. Dom is the glue of "La Familia", and nobody would want to see the family broken up permanently. It would also be desperately sad to see Little Brian left without a parent in his life. The others in the crew would undoubtedly see that he was cared for, but he would never be the same if he lost his mother and his father. Little Brian will have a hard enough time already after his mother's death, and Dom dying on top of that would be too much.
Killing Dom Would Bring His Fast & Furious Superhero Arc To An End
While it is no longer likely to happen, killing Dom Toretto in Fast and Furious would fit as a conclusion to his superhero-like arc. Dom is all about taking care of the people he loves no matter the cost, and there are few sacrifices greater than one's own life. Dom would undoubtedly be willing to die for his family, and him making the ultimate sacrifice would be one way to fittingly conclude his story. As a superhero-like character, Dom's story ending with his death could symbolize everything he has embodied throughout the franchise, but again, it's unlikely to happen now that he has a son.