ATLANTA -- Of all the decisions the Mets must make this winter, some of the most difficult will revolve around their so-called “core” -- a group of homegrown players that, since late in the 2018 season, has constituted the bulk of their lineup most nights. When Pete Alonso, Michael Conforto, Jeff McNeil, Dominic Smith, Brandon Nimmo and J.D. Davis began gelling the following summer, that group seemed prime to lead the Mets to perennial postseason success.

It didn’t happen. And now, as Mets president Sandy Alderson put it this week, that core is “eroding.” Conforto is due to become a free agent after the season. Nimmo, who homered twice in the Mets’ 4-3 win over the Braves on Friday, is a year away from joining him. McNeil, Smith and Davis are all coming off down seasons. Combined, those issues suggest that the Mets’ core might never have been as stable as team officials once hoped.

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“Any time you finish a season, what you really have to do is reevaluate each player and try to decide who they really are,” Alderson said. “That would be true in a season where the player underperforms. It might be a season in which a player overperforms. You really have to do an evaluation of what, predictably, will happen in the future.”

In the case of Conforto, such evaluations could determine whether he returns to Flushing. The Mets will need to acquire at least one everyday outfielder this winter; Conforto is certainly an option to come back, but the team could also look elsewhere -- at Starling Marte, for example, or Nick Castellanos, or any number of other free agents or trade targets.

Then there are McNeil, Smith and Davis, none of whom have obvious starting jobs on the 2022 roster. All could potentially reprise their roles, of course -- Smith in left field, Davis at third, McNeil at multiple positions. But if the Mets want to make significant changes to an offense that consistently ranked in the bottom five in the Majors in runs per game all season, then those positions will be the easiest for them to shuffle.

The Mets already shook up their offensive core to a small extent last offseason, dealing Amed Rosario to the Indians in a package for Francisco Lindor. Additional changes could occur soon.

“There’s a lot of questions that need to be answered,” Alonso said Friday when asked why the Mets’ core hasn’t lived up to its potential. “For me personally, I want to be able to get the team over the edge. I want to be one of those cornerstone guys that’s on the field dogpiling and champagne showering at Citi Field. I want to be that.”

During a 10-minute interview regarding the state of the team, Alonso repeatedly blamed himself for the Mets’ failures. But he is, statistically, the least of their problems. The Mets’ healthiest and most consistent offensive player all year, Alonso bounced back from a disappointing 2020 to bash 37 homers. Of New York’s core hitters, Alonso and Nimmo are the surest bets to return -- the former at first base, the latter at one of three outfield positions.

Beyond them is anyone’s guess, realistically falling under the purview of the Mets’ incoming -- but as-yet-unknown -- president of baseball operations. One of that person’s first tasks will be determining which hitters should stay and which should go.

“I feel a little bit of disappointment in that, because I enjoy these guys so much,” Nimmo said, acknowledging the inevitability of change. “I felt the same way as everyone else that this team was going to be built to win here. Obviously, that didn’t happen.”

Alonso, for his part, still believes the Mets possess the infrastructure to be a championship-caliber club as soon as next season -- a lofty goal, considering this core group has never finished above third place in the NL East. But it is a goal to which the Mets will cling until their offensive core either wins … or dissolves.

“I love playing for New York. I love playing for the Mets. I love representing orange and blue,” Alonso said. “But I hate to lose. This isn’t where any of us want to be right now, going home on Oct. 3. We want to be going home holding up a trophy and being able to join a parade.”