I like your alternative story line and it’s entirely possible we’ll see some form of it in episode 8. I agree that it’s tough to squeeze two major story lines into one movie, but I don’t think they really had a choice because…
1. Rey needs Solo to guide her to Maz Kanata and the light saber
2. Solo has a special feeling for Rey (we’ll know why in episode 8), which inspires him to try to rescue her (and save the galaxy from the Starkiller base)
3. As Tommy Branagh points out, Solo’s attempt to bring his son home helps make Kylo Ren a much more important and conflicted character
4. There’s a crazy symmetry to having a son kill his father after a father saves his son’s life (in ROTJ). I wish it would have happened in episode 8, because this moment feels like it should have been the absolute low point of the trilogy, paralleling Luke Skywalker finding out Darth Vader is his father. For us older fans, it was like an emotional haymaker should have mattered. Instead it almost felt like just one more dead guy in a huge battle.
5. Even if it isn’t the best plot structure, ignoring the overwhelming desire by fans to see Han Solo again and to pass on the torch might have killed the franchise, and
6. I really felt like this was a reboot of “A New Hope” for the kids of today. Watching the original trilogy almost feels quaint now, because of the limited special effects and the pacing of some shots. Writers and jaded fans might complain about seeing another Death-star like plot line, but I tried to see it through a child’s eyes today. They wouldn’t be deconstructing the movie like we are. They would be enthralled with the action, while the old fans enjoy the homage scenes. (I loved the initial chase scene where Rey flies through the crashed destroyer followed by tie fighters — I remember playing a video arcade game in the 80’s that traced the exact same path!)
With regard to your idea that Han Solo should have sacrificed himself in ROTJ, I totally disagree. Just like there shouldn’t be two story lines competing in The Force Awakens, you can’t have two of the same major anything. The most important story arc of the entire trilogy is completed when Darth Vader sacrifices his life for his son. Killing Han Solo in this movie would have detracted from Vader’s final redempiton.
In addition, Solo needs to survive in order to have kids with Leia to continue the Star Wars universe.
Finally, when parents lose a child, it often leads to the breaking of the marriage — the shared memories are too painful. I could easily see Solo — like a recovering alcoholic who goes on a drunken binge in response to a personal tragedy — fall back into his old ways as a smuggler and inveterate gambler.