By Tony Massarotti, Boston.com Columnist

Just how important is Rajon Rondo to the operation of the Celtics?

Maybe now we’ll all get our answer.

And so after all of that, after all of the discussion about extending the window of the Kevin Garnett Era and the best way to build the Celtics, Rondo is the one lost to a season-ending injury, the Celtics revealing on Sunday that the point guard tore the anterior cruciate ligament in his right knee during Friday’s devastating double-overtime loss to the Atlanta Hawks. What a truly dispiriting defeat that was. The Celtics subsequently went out on Sunday and defeated the Miami Heat without the man deemed to be their leader, and story lines were butting up against one another like sections of the parquet floor.

Ray Allen came. Rondo went. The Celtics plodded on.

Small samples and large samples are entirely different things, but the Celtics so far this season are 18-20 with Rondo, 3-3 without him. During last year’s pivotal Game 2 against the Atlanta Hawks in the first round of the playoffs, the Celtics won without their multitalented point guard. All of that has only fueled the debate about Rondo as much as it has about his position, about the value of offense defense and everything in between.

Pick a side. The Miami Heat won the NBA championship last season with Mario Chalmers at point guard. The Chicago Bulls crumbled without Derrick Rose. In the end, both those stories were more about the star player (i.e. LeBron James) on each team more than they were about the position he plays, which brings us back to Rondo and his admittedly unique skill set.

Just how much is he really worth?

On the surface, we can all make snap judgments about how Rondo’s absence will impact the Celtics. In theory, their defense could improve. Their half-court offense could suffer. Their rebounding will take a reasonably sized hit and their ball-handling an even bigger one, the latter of which could be rather ugly if and when the Celtics reach the postseason.

Now the facts: With Rondo playing a team-high 37.4 minutes per game this season, the Celtics are under .500. They rank 21st in scoring offense and 11th in scoring defense, the latter of which improved only after Avery Bradley returned. They are a relatively mediocre 12th in the league in turnovers.

By now, Rondo’s shortcomings are extremely well-known. No matter what the numbers say, and despite some improvement, he is not a particularly good shooter. He plays cheat defense and is lazy on the ball. The Celtics offense sputters when Rondo is not attacking the basket, and he seems interested in playing some nights, disinterested in others.

From the very start of this season, the Celtics have all but put up lawn signs in the campaign to anoint Rondo as their leader. Unsurprisingly, they have been inconsistent and erratic. Too often, the Celtics have looked like they are coasting, particularly on the defensive end of the floor. Paul Pierce has looked old. Kevin Garnett has played reasonably well, but often seems to be on his own, minute-managing program.

So here’s the real question: With Rondo out, does the hierarchy of the Celtics change? Are Garnett and Pierce forced to reclaim the leadership roles they ceded, thereby giving the Celtics more of the day-to-day consistency the team clearly needs? Or does everyone now take a hands-off approach, leading to an on-court disintegration that forces Ainge’s hand as we approach the trading deadline?

Fascinating, to be sure.

For what it’s worth, the Celtics went into New York without Rondo this season – he was serving yet another one-game suspension – and won. They played against the Heat without him on Sunday – and won. Pending the return of Rose in Chicago, Miami and New York currently stand as the two best teams in a weak Eastern Conference, and there is at least some evidence that the Celtics can still compete with both.

Does this mean the Celtics can beat the Heat in a seven-game series? Hardly. But that was true when Rondo was healthy, too. Nobody ever really looked at this season and expected the Celtics to defeat Miami in the postseason. Most of us just believed that the Celtics might have what it takes to beat just anybody else in the Eastern Conference.

Without Rondo, that task now is obviously more difficult. They will miss his talent. But Rondo’s leadership skills always have been in question, and the simple truth is that the 2012-13 Celtics have been disjointed and fractured. They have not often looked like a team.

Now, perhaps, they have a chance to become one.