Unfortunately, Missy is headed for a rough patch. George's impending Young Sheldon death will be difficult for the Coopers, but it will be particularly taxing for his only daughter considering her close relationship with him. In The Big Bang Theory, she was revealed to be on the cusp of separating from her husband while she was pregnant with her second child. Luckily, after everything she went through, Young Sheldon revealed that Missy lived happily after The Big Bang Theory. According to Sheldon in his narration, Missy is empathic and agreeable and can find friends easily, which means she has a loving family and friends.
She ultimately gets remarried and has a loving family after her separation from her first husband. Specifics of her post-The Big Bang Theory fate weren't revealed, but the spin-off prequel can continue to reveal new information about Missy's future. This will be especially pivotal if CBS plans to tackle more of her personal arc on Young Sheldon.
Despite Young Sheldon's growing popularity, it has a pre-determined end thanks to The Big Bang Theory's established continuity. While the flagship series continued to tackle Sheldon's arc in Pasadena, not much is known about what happens to his family after George's tragic death. When Georgie appeared on The Big Bang Theory, however, he briefly talked about how they coped after the Cooper patriarch's demise. Mary, apparently, was too overwhelmed by grief, while Missy was "just a dumb teenager" back then.
It's uncertain what Georgie exactly meant when he described his sister like that, but it's possible that she went through a rebel phase as her way to cope with the loss of George. However, in season 6, Missy did start acting out, and it seems that this is where her journey from a promising young woman to someone who never found her way started. When Sheldon decided to tell on her to protect her, it caused a big fight and the two of them seemed unwilling to recover from it. However, that was when the tornado struck. It was here that Missy, in tears, apologized to her dad for how she was acting and seemed ready to turn things around.
Looking back, it's quite difficult to believe that Young Sheldon's Missy turned out to be the least successful Cooper sibling on The Big Bang Theory. The Cooper daughter has great potential on the prequel sitcom, it's sad to know that she never reached her full potential. At this moment with the tornado, it was her dad that she broke down to and started a redemption phase with. With George dying very soon, this could be what finally destroyed Missy and started her eventual downward momentum. At the very least, she ended up having a great personal life — something that hopefully Young Sheldon season 7 can reveal more of through adult Sheldon's narration.