With Better Call Saul rapidly catching up to Breaking Bad's story, the upcoming Breaking Bad movie can effectively end the Better Call Saul TV show in the franchise's future. Fans know that Jimmy McGill ultimately transforms into Saul Goodman in the Breaking Bad TV show, but his association with Walter White and Jesse Pinkman eventually forces him to move to Nebraska and adopt the name Gene Taković, who manages a Cinnabon in the local mall.
Because the endpoint for Jimmy’s story arc was defined halfway through Breaking Bad season 2, Better Call Saul should conclude with Gene's future in Nebraska. This is the part of Better Call Saul that represents the great unknown, and it’s every bit as fascinating as Jimmy’s transformation into Saul Goodman. However, it just hasn't been explored in much detail yet. It's unclear where Jimmy's story is going to go in Better Call Saul season 5 or what happens to Gene in the future, but these are both ideas that can be tackled in the upcoming Breaking Bad movie.
The Breaking Bad movie that Vince Gilligan is writing, which sees Aaron Paul return as Jesse Pinkman, will continue the story that left off with Breaking Bad's series finale. That means it can reveal what happens to Jesse after he speeds away and leaves Walter White behind. While the Breaking Bad movie can give Jesse a happy ending, there’s also an opportunity for Gilligan to kill two birds with one stone and unite both Breaking Bad and Better Call Saul.
It would be quite easy for Better Call Saul to link to the Breaking Bad movie. Gene is still somewhat connected to the world of Breaking Bad - indeed, it’s a connection he lives in fear of - and alongside his past as a lawyer, there’s potential for him to hear about or even get caught up in whatever’s happening with Jesse Pinkman. After Better Call Saul's season 4 finale, only so much can happen before Jimmy McGill inevitably becomes Saul Goodman and catches up to the Breaking Bad timeline. So, Better Call Saul could theoretically end with season 5. After all, Breaking Bad was only on the air for five seasons.
In that case, rather than continue Jimmy McGill's story as Saul Goodman, the series can end with Gene's story in the future in Nebraska. It would allow Better Call Saul to keep its ultimate focus on its titular character until the very end, and then the Breaking Bad movie can show audiences exactly what happens to Gene. It gives that character a sense of closure, but is also a means of fleshing him out further in a way those vignettes at the very beginning of each season don’t allow for. On top of that, it’d be an added hook for the movie. Simply being Jesse’s story is good in itself, but if you can then link that together with what happens to Jimmy/Saul/Gene in the very end, and bring everything - Breaking Bad, Better Call Saul, and the Breaking Bad movie - full circle and tied off neatly, then that’s a deal Saul Goodman wouldn't need to con people into buying.