While to some players the true protagonist of The Last of Us Part 2 was still Ellie, it is also true that both Abby and Lev had enough screen time to become fully fleshed-out characters, and quite compelling ones at that. However, when the game starts, there is nothing to hint that Abby will be a fully playable character, and players delving into the game without reading anything about it most likely thought that the story would revolve around Ellie and Joel instead. That is still true in a way, even if the beloved protagonist of the first The Last of Us game is brutally murdered merely an hour into The Last of Us Part 2, and there are two details about this that many fans found disheartening.
The first is that Joel's death is raw and unsettling, and it comes as torture both for the characters involved and the players alike, who have to watch a character they learned to love throughout the first game being beaten to death. The second detail is that Joel is killed by Abby, who then lives on to be the deuteragonist of The Last of Us Part 2, which hits harder because Joel saved Abby's life moments before his death. This combination of things led to a mixed reception for the game that was based around the fact that players were not happy with having to control Abby or hurt other "good characters." However, that was the entire point of this game.
Abby Acts as The Last of Us 2's Model for Change
The Last of Us Part 2 is a game where there are no clear protagonists nor good characters. Rather, the stars of the show are violence and revenge, with the concepts of good and evil greyed out as the story unfolds. Killing Joel was the inciting incident for the story in the game, and what comes next is something that comes purely out of the complex social dynamics and psychological traits of the characters. Players tend to automatically be on Ellie's side because they know her, they played as her in the first game, and they watched her change and mature over time. Most importantly, they tend to be on Ellie's side because Abby kills Joel.
This enacts a vicious cycle of violence and revenge where there are no winners, but rather survivors who have to learn to live with what they have done and what was done to them by others. There are plenty of factions in the world of The Last of Us Part 2, and yet the game makes an effort trying to explain why factionalism is at the very core of the aforementioned vicious cycles, meaning there shouldn't be an "us versus them" mindset. That's why Naughty Dog made the bold decision to have The Last of Us Part 2 be a game that offers to its players both Ellie's view of things and also Abby's.
In perhaps one of the most interesting point of view switches in the history of video games, The Last of Us Part 2 lets players control Ellie for the first half of the game, only to make them play as Abby instead moving forward. This is where they learn about Abby's reasons for killing Joel, and the game delves into the life of this complex character, who also is victim to the mindset of factionalism for a good part of The Last of Us Part 2. That changes because of the events that ensue, which see Owen, one of the people she cares about the most, saying that he is done with fighting the Seraphites. Abby herself is then saved from death by two Seraphites, Yara and Lev, making her move away from factionalism.
Abby forms a strong bond with Lev, and she starts caring more for a select few people than her own faction, effectively deserting the Washington Liberation Front. Abby and Lev eventually lose everyone else they care about, with Lev accidentally killing his mother and Yara dying in order to protect him. Abby loses everyone in her group, including Owen. In Abby's case, her friends are taken out by Ellie and her group in the first half of the game, further showing how certain actions can be justified in one's mind because of that person's biases.
Where Abby and Lev's Story Ends, and Where it Could Pick Up In The Last of Us 3
However, Abby and Lev's story is far from over, as they eventually leave Seattle for good. A year after the events thus far, the duo reaches Santa Barbara and trades goods in order to find leads about the rumor that Owen once shared with Abby about the Fireflies regrouping somewhere in that area. Abby and Lev learn that the Fireflies have regrouped on Catalina Island and are prepared to reach them as soon as possible, but soon after they are captured by yet another The Last of Us Part 2 faction - the Rattlers.
The Rattlers enslave Abby and Lev, and when the two try to escape in an act of defiance, their captors tie them to poles on the beach and leave them to the elements and starvation. That's when something seemingly impossible happens, and Ellie - who had been tracking Abby up to that point - finds her and Lev and frees them. Ellie is not ready to let go, forcing Abby into a fight even though she refuses to give in. Eventually, the former overpowers the latter and proceeds to drown her. However, a vision of Joel stops her, and Abby and Lev are finally free to go.
As such, their story can go pretty much anywhere if they were to be featured again in The Last of Us Part 3, for which Neil Druckmann already has a plot outline ready. Abby and Lev know the Fireflies are regrouping, and they spent a lot of energy and resources to obtain that piece of information. Still, after all they've been through in The Last of Us Part 2, it would be understandable if they chose to instead find a safe place and live a quieter life. This could at least be the case at first because both of them are extremely weak at the end of Part 2, and they can't really know what lies in wait on Catalina Island.
Abby's story may be concluded, as fans know that she is reuniting with the Fireflies alongside Lev. Still, that was the pair's goal before being tortured by the Rattlers. As such, The Last of Us 3 could make a final effort to further validate the point made in The Last of Us 2. Abby and Lev could change their minds and be done with all factions, including the Fireflies. After all, the only real link between the pair and the organization is dictated by Abby's past, which she spent the entirety of Part 2 trying to put behind her. With Abby's character arc already being more positive than that of Ellie's, seeing her move on from groups to focus on living a happy life would be fitting.
The Last of Us Part 2 is available on PS4 and PS5.