While very little is known about the Mass Effect mods saving characters, BioWare's epic science-fiction franchise is not shy about killing off beloved mainstays, including Commander Shepard themselves, who is killed in almost every ending of Mass Effect 3. However, it is possible for them to return in Mass Effect 4, and there are a few ways that this could play out.
Much ink has been spilled about Mass Effect 3's controversial ending, with many criticisms being raised regarding its lack of consequence, restrictiveness, and anti-climactic nature. The ultimate showdown with the existential Reaper threat turned out to be much less focused on combat than some anticipated, with Shepard interfacing with an ancient consciousness and choosing between three major options, which is part of what made some players feel that Mass Effect 3's choices didn't really matter. The first option is Destroy, which wipes out all synthetic life in the galaxy, causing widespread suffering but effectively eliminating the Reapers. Control is another option, which sees Shepard assume complete authority over the Reapers, using them to repair the damage done to Mass Relays and human settlements. Choosing the Synthesis option results in a new race emerging, one that is a blend of human and synthetic, ushering society into a strange, mysterious era.
These are the three main endings, but each has a number of deviations that depend on various choices made throughout the course of the game. In one particularly difficult to achieve version of the Destroy ending, it's hinted that Shepard is still alive. While there has been no confirmed canon ending to Mass Effect 3, this specific version would leave the door open to the most possibilities in a future game. A merchandise listing on BioWare's website suggested that Commander Shepard could return in Mass Effect 4, and making this ending canon would allow for that.
How Shepard's Survival Would Shape Mass Effect 4's Story
Because Shepard can only live via the Destroy ending of Mass Effect 3, their inclusion in Mass Effect 4 would rule out the Synthesize and Control endings. This would mean that the Reaper threat has been eradicated and that no new race of machine-human hybrids has arisen. Through these circumstances, a new antagonistic force could come to power, or some remnant of the Reapers could still need to be stamped out.
Shepard surviving would also have implications for the timeline of the series. A 2020 teaser for Mass Effect 4 suggests that Liara is still alive, but Asari live for hundreds of years, so it's very possible that the new game could take place long into the future. However, Shepard is only human with a few cybernetic enhancements that give him an edge over highly effective human Mass Effect characters like Ashley and Kaiden. Therefore, if Shepard does indeed live on in Mass Effect 4, it would need to take place shortly after the events of Mass Effect 3 and long before Mass Effect: Andromeda. Were BioWare to take this route, it would allow for the return of several other beloved characters as well.
BioWare quickly removed the mention of Shepard on its merch site without comment, so the fate of the legendary commander ultimately still remains to be seen. Because they played such an instrumental role in the outcome of Mass Effect 3, Shepard surviving would have a major impact on the overall premise of the next game, so this isn't a story decision the game's developers will probably make lightly. Whatever direction Mass Effect 4's story takes, the life and decisions of Shepard are sure to influence it.