Mom initially shows Christy and Bonnie Plunkett's journeys as they try to stay sober and turn their lives around. Things are not that easy between their rocky relationship and Christy's complicated dynamic with Violet, Roscoe, Baxter, and Candace. However, somewhere along the way, Mom stopped focussing mainly on Bonnie and Christy with their familial issues at the forefront and broadened the spectrum to introduce Marjorie, Jill, and Wendy, three other recovering people with alcoholism that join their meetings.
Mom became about friendship and chosen family, with Adam and Tammy eventually joining the close-knit group as well. Running for eight seasons, the show had to come up with a finale due to an unexpected cancellation by CBS. Thus, Mom worked to give its main characters an ending that would fulfill both them and the audience. While they succeeded in some ways, other characters either had an unnecessary storyline or were left without a solid conclusion.
Wendy
Wendy has been a main member of the group for years. Yet, she got the least amount of central storylines and character development out of all the women. While Wendy does have funny dialogue, she seems to exist mostly to be pushed around by the rest of the group. Wendy tends to bounce between passive and trying to make her voice heard but doesn't last very long.
In the series finale, Wendy doesn't even get an ending dedicated to her. There is not anything that provides information about whether she will be moving forward. Instead, Wendy stays relatively the same with the bonus of having the show's final line.
Adam3
Something does happen with Adam in the finale, but, unfortunately, it's bad news. As it turns out, years of smoking caught up to him, leaving him sick in the early stages of cancer. While it appears that the doctors caught it early enough to save Adam, it is still a sad conclusion.
In fact, the storyline comes across as being less about Adam and more about Bonnie's reaction to the news about Adam. Adam has been involved in the show too long for his final storyline to be used as a plot device.
Tammy
Mom repeatedly recites Tammy's development in the final episode, continually mentioning her business with Bonnie and her new relationship. Tammy has tried to make amends for her past actions and walk a more truthful path.
Tammy even has a brief reunion with the judge who sentenced her to prison and happily told him that she had gotten her life together in addition to getting out. Her business is successful, and it looks like things will be working out for her.
Marjorie
Having made up with her son, babysitting her grandchild, and receiving an award where her son had nominated her, Marjorie's ending is quite nice, especially considering how those relationships had been previously.
Marjorie's award even triggers unexpected emotions in Bonnie, having her reveal how grateful she is to Marjorie for how much she has done to help over the years. In the end, Marjorie is there for Bonnie to hear about Adam and is a calm presence where the group needs one.
Christy
Christy Plunkett was one of Anna Faris' best roles, and her choice to leave Mom before the eighth season left Christy's future uncertain. Luckily, the show's creators found a way to write Christy off in a way that showed she is still in a good place and following her dreams at law school.
Becoming a lawyer had been a longtime subplot for Christy as she strove through school to reach her goal of enrolling in law school, gaining jobs and internships, and eventually becoming a lawyer. While Christy's choice to move away happens off-screen, it is still an essential decision for her and something that allows her ending to be worthy of all she had been through.
Jill
Jill's struggles for a long time involved getting sober, dealing with the fallout from her divorce, and wishing to have children. By the series finale, Jill is happily sober and has strong friendships with Christy, Bonnie, Marjorie, Tammy, and Wendy. She reunites with Andy on the romantic front, and the two even get married in the final episode.
But, before that, the duo learns they are expecting a baby. Jill had wished for these things for a long time, and it was a great and exciting way for her to receive everything she wanted before the final credits rolled.
Bonnie
Allison Janney's Bonnie Plunkett had the biggest character development out of everyone. Bonnie has commented several times on the crazy things she has done while drunk, high, or as a way to try and get drunk and high. Bonnie's relationship with Christy was back and forth for years before the two got on decent footing. The two are stronger than ever by Christy's final episodes, and even after she left, Bonnie still speaks to her on the phone.
Bonnie's relationship with Adam was a big step for her as well. When it comes to sobriety, Bonnie has had her struggles, but ultimately proved that she wanted to be sober and worked to do so. She has even become a sponsor to others and looked out for another mother-daughter duo. The series finale constantly refers to the major character development Bonnie has been through as she has not been worried about herself in the occurring activities but concerned for others. She had even spent time in therapy to work on herself!