After his postgame press conference, upon first learning of Celtics point guard Rajon Rondo’s season-ending ACL injury, Heat coach Erik Spoelstra pulled a reporter aside to ask, “Really?”

The shock in Spoelstra’s voice begged the same question everyone else asked as the news spread like wildfire through the Garden on one of the most bizarre afternoons in the building’s history: Where the hell do the Celtics go from here?

One thing’s for sure. As Heat superstar Dwyane Wade said, “It sucks, man.”

“I think it sucks,” reiterated reigning NBA MVP LeBron James. “It's terrible.”

It sucks for the Celtics, who must finish the season without the guy LeBron once called the “the head of the snake,” and it sucks for the NBA, which lost perhaps its most enigmatic and exciting postseason star.

Whether or not the rest of the Celtics can even make the playoffs without him remains to be seen. Sunday’s surprising 100-98 double-overtime victory against Miami snapped a six-game losing streak and improved the C’s record to 21-23.

Even with Rondo, the Celtics dropped below .500 midway through the season and faced the reality of holding off a 76ers team that stands to add Andrew Bynum down the stretch of a run for the eighth seed in the Eastern Conference.

That leaves Celtics president Danny Ainge with two options: a) Pray Rondo becomes the new face of Bill Simmons’ Ewing Theory, or b) Start planning for the future.

Under the Ewing Theory, the Celtics would somehow play inspired basketball in Rondo’s absence and climb the conference standings. Considering the seven teams trailing Miami are all within 6.5 games of each other, it’s not entirely impossible.

Despite his league-leading 11.1 assists per game and five triple-doubles, Rondo hadn’t met expectations that had risen to MVP candidacy proportions this summer. The Celtics are 3-3 without Rondo this season, including victories over the rival Knicks and Heat, and they’re 18-20 with him.

“It just puts this team and the rest of these guys in position to be ready to step up,” said Celtics captain Paul Pierce, who had a triple-double of his own in Rondo’s stead. “Tonight was a perfect example. We showed with or without Rondo we still have the depth to compete with anybody.”

As he did against the Heat, Pierce becomes facilitator in place of Rondo. Courtney Lee takes his place in the starting lineup, forming an impressive defensive backcourt with Avery Bradley. And Jason Terry, Leandro Barbosa and Jeff Green assume some of the scoring responsibility. Easier said than done.

“Nobody’s going to walk through these doors and save us,” admitted Kevin Garnett. “We have to save ourselves. We created this mess, so we have to work our way out of it. I told you we have a bunch of fighters in here, a bunch of guys who are willing to work and get down and actually put the work in. That’s what we’ve always been since I’ve been here under the Doc [Rivers] regime.

“Today was hard,” he added. “I’m not even going to front. Today was hard.”

There’s no doubt a team led by Pierce and Garnett will continue to fight, but how far can the two aging veterans carry the Celtics without Rondo? Don’t rule out another appearance in the second round; after all, the C’s made the Eastern Conference semifinals without Garnett in 2009.

“You can write the obituary,” said Rivers. “I'm not. You can go ahead. But I'm not. We won tonight, and so the way I look at it is: We are going to stay in there. In my opinion, we’re going nowhere.”

Still, at some point, the Heat stand in their way, and as many times as Pierce claimed, “We still like our chances in the Eastern Conference,” it took a triple-double from the Celtics captain and a monster double-double from Garnett to hold the Heat off in two overtimes at home on Sunday.

Ainge can’t possibly believe this Celtics team can win a seven-game series without the only serious mismatch they have against the Heat. After all, Rondo either scored or assisted on 140 of the C’s 245 field goals (57%) in their seven-game Eastern Conference finals series last year. In other words, if Ainge is being honest with himself, he must start thinking about next season and beyond.

As Wade said, “They haven't played without [Rondo] much, but he's a playmaker for this team. He pulls most of the triggers for this team. He pretty much does it all. He's a triple-double in the making.”

Without Rondo, should the Celtics slip further in the standings before the Feb. 21 trade deadline, Ainge must seriously consider dealing Pierce and any other piece that might land young talent or draft picks in return, settling for the lottery this spring and rebuilding around Rondo, Bradley and Jared Sullinger.

Otherwise, he’s hoping Rondo returns to form at some point next season (see: Rose, Derrick) and praying both Pierce and Garnett produce at ages 37 and 38 while surrounded by the same cast of characters who haven’t shown an ability to win on any consistent basis this winter.

Of course, dealing Pierce is no small task. The ramifications of trading the cornerstone of the game’s greatest franchise would be severe, and Kevin Garnett’s retirement could be the first domino to fall.

As hard as that might be, even though they slayed the dragon Sunday, without Rondo this team is no longer built to beat the Heat and no longer a title contender. All the grit and balls in the world won’t change that.

“He's a great player, and he really is the leader of this team,” added Wade. “Obviously, guys are going to have to step up for them, but this year they lost the leader of their team, so it's tough for the game to lose a player like Rondo, but especially Boston.”

Which is why Spoelstra’s one-word question rang so true in the hallway of a Garden that had grown eerily quiet once the deafening crowd subsided from booing Ray Allen, applauding a one-armed soldier who performed 26 pushups at midcourt, cheering Rondo’s appearance on the Jumbotron and exploding for Pierce’s go-ahead jumper in the final minute of double overtime.

“Really?”

After injuries to Garnett in 2009, Kendrick Perkins in 2010 and -- to some degree -- Shaquille O’Neal in 2011 and Pierce in 2012 all cost the Celtics shots at multiple titles in this run, a fluke ACL tear to the one guy who seemed so indestructible -- the 27-year-old kid who once played through a horrific elbow injury -- might have finally driven the stake through the heart of the champion.

Really?