After a series of questionable decisions, which were part of her rebellious phase, Missy seemed to have finally regained her senses and realized the error of her ways in the Young Sheldon season 6 finale. While on their way home from dropping off Sheldon and Mary at the airport, Missy and George were forced to leave their car and lay flat on the side of the road as the Medford tornado passed. After their near-death experience, Missy suddenly broke down and apologized for acting up. Considering Missy's track record, it was clear that she was only rebelling as a way to get back at her parents for constantly ignoring her.
Missy's tearful apology in the Young Sheldon season 6 finale appeared to be the beginning of her redemption arc. That being said, a CBS marketing video for Young Sheldon that updates fans about the Cooper kids' current situations states that Missy is still "in her rebellious phase." This means that coming into season 7, Mary and George's only daughter will continue to wreak havoc despite previously claiming that she will finally make amends and behave correctly.
While Missy continuing her rebellious phase is bad news for the Coopers, it's a good development for the future of Young Sheldon.
Beyond the show's guaranteed run, this plot can also be the springboard for its future. Despite having a titular character, Young Sheldon has become more of an ensemble series, with an increased focus on the rest of the Coopers.
The Big Bang Theory offered an idea of what the future holds for the Cooper kids. While Sheldon excelled as a physicist, eventually winning a Nobel, and Georgie became a successful business owner, Missy spent her time in a miserable marriage with an unfulfilling job.
Exploring Missy's rebellious arc could offer an explanation for why she never reached her full potential. Although Young Sheldon started as an origins story for Sheldon, the increased attention given to the rest of the Coopers, particularly his siblings, means that it could also function as a prequel for their The Big Bang Theory stories.
If Missy continues to act up and stray from the straight path in Young Sheldon season 7, there are several benefits to the franchise's storytelling. Firstly, ensures that Missy will not be overlooked in the prequel moving forward, and she will continue to have her personal arc, similar to what Young Sheldon has done with Paige.
CBS can do this by properly ending Young Sheldon after its titular character moves to Pasadena. This way, it isn't further breaking The Big Bang Theory. However, similar to what ABC did when they spun off Roseanne into The Conners (although having a very different context), CBS can launch an offshoot of Young Sheldon with The Coopers. The ensemble will follow Missy and the rest of the Coopers as they continue life in Texas after Sheldon moves out. Since The Big Bang Theory didn't reveal much about this time in the Coopers' history, CBS has more creative wiggle room to craft its story.