The Sixers are facing their most important games in a quarter-century. Maybe longer.

Every sports franchise has a few inflection points in its history, and the 76ers are approaching one. It’s not just that their Eastern Conference semifinal series against the Celtics is tied at two. It’s not just that a berth in the conference finals — where the Sixers would be assured of home-court advantage against a lower-seeded opponent — is at stake. It’s that the complexion of their present and future and the perception of their two most important players are likely to change based entirely on the outcome of this series. If you think that assertion is an exaggeration, consider the following factors that are at play ahead of Tuesday night’s Game 5 at TD Garden.

Let’s assume, for the sake of argument, that the Sixers turn their dramatic 116-115 victory Sunday in Game 4 into an emotional springboard, beat the Celtics in six or seven games, and advance to take on either the Heat or the Knicks for the right to go to the NBA Finals. They would be heavy favorites in that conference-final matchup, and barring a collapse similar to the one they experienced in 2021 against the Atlanta Hawks, they’d have a shot to win their first championship since 1983.

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A berth in the Finals would do more than shepherd the team’s fans on their most thrilling ride since Allen Iverson was high-stepping over Tyronn Lue in June 2001. It would validate the all-in approach that Daryl Morey took in building this roster. Not that Morey had much choice. The team’s centerpiece, Joel Embiid, has been so prone to injury and illness over his career that it would have been too risky for Morey to say, Well, Joel is just in his late 20s. We have time.

» READ MORE: The Sixers were out of gas, out of luck, out of time. Now, they’re alive.

Actually, the Sixers don’t have time. As this postseason has reaffirmed, Embiid is always one tumble to the court away from a tear or a strain that saps his short- and long-term effectiveness and threatens to keep him out of the lineup. So Morey has acted accordingly. He traded for James Harden and De’Anthony Melton and signed P.J. Tucker. No more waiting for Matisse Thybulle to improve his jump shot. Nope, trade him for Jalen McDaniels, who if nothing else isn’t completely useless on offense. Go after the championship right now while Embiid is in his prime, while Harden is on the back edge of his, while Tyrese Maxey and Tobias Harris can win you a game on the right night.

Now, let’s assume, for the sake of argument, the opposite outcome: The Celtics bounce back from their late-game mistakes Sunday, remember they’re the better overall team, and win this series. Morey might be inclined, based on the contract statuses of a couple of core veterans, to make major changes to the roster even if the Sixers reach the Finals. But if they don’t, those changes would be imperative, right? Even if Harden opted in for the final year of his deal, would it make sense for the Sixers to bring him back? Harris is entering the final season of his max contract; what might another team be willing to give up to get him? Would Morey and ownership replace Doc Rivers? I wouldn’t — Rivers has been fine, and the continuity of sticking with a proven coach would be a benefit — but would they?

» READ MORE: Resetting Sixers-Celtics series odds after four games

The Sixers’ two most important players are, of course, Embiid and Harden, and each has a significant aspect of his “legacy” at stake here.

For his back-to-back scoring titles and his MVP award, Embiid has recently garnered plenty of positive comparisons to Wilt Chamberlain. But the longer he goes with each of his seasons ending in disappointment, the more he invites a less-flattering one: a pair of post players who were dominant but whose teams rarely were. Chamberlain put up ungodly numbers and won a few championships, but those achievements couldn’t compare to Bill Russell’s contributions to the Celtics’ dynasty. Without a deep postseason run, Embiid is sure to be viewed the same way as the passage of time strips away any context or excuses. (e.g. Yeah, but he had to deal with Ben Simmons!)

As for Harden, he’s similar in certain respects to Embiid: so much skill, so many individual accomplishments, no parades yet. But unlike Embiid, who has forged a tight bond with Philadelphia, the Sixers, and their fan base, Harden has placed a burden on his own back: that of a basketball mercenary, willing to pout his way to more favorable conditions for himself. He did it in Houston. He did it in Brooklyn. And already there have been rumbles and rumors that he will do it here. His performances in Games 1 and 4 against the Celtics mitigate that image only so much.

It has been 40 years since the Sixers last won an NBA title. Over those four decades, they have reached the conference finals exactly twice: in 1985, when the Celtics waxed them in five games, and in 2001.

» READ MORE: Philly Tough: Joel Embiid’s heroic game & James Harden’s bounce-back evens series. Now, do it again.

If they were to lose to Boston now, it would mark the sixth consecutive year that they qualified for the playoffs but couldn’t advance past the second round. Their history is more star-crossed than storied, and franchises have overhauled themselves for less.