Though ratings for Thursday’s broadcast will be telling, there are indications that NBC comedy “Community” will emerge from its life-support existence with a fourth-season renewal, in a manner that speaks to the power of on-air network promotion, a passionate online following and the importance of scheduling even in the DVR age.

NBC sent “Community” on a three-month hiatus in December, setting afire speculation that the imaginative but aud-challenged comedy from showrunner Dan Harmon was nearing an end. But over a 48-hour period last week, its outlook turned decidedly sunnier.

On March 14, Sony Pictures TV announced it had sold off-net rights for the first three seasons of “Community” to Comedy Central. Then a day later on NBC, “Community” rose to a 2.2 rating among viewers 18-49 (nearly 50% higher than its previous episode) and was No. 1 at 8 p.m. among adults and men 18-34, topping Fox’s “American Idol” and March Madness on CBS.

Suddenly, the laffer had momentum beyond its famously fervent if finite fanbase. The questions for “Community” — and for other shows in similar straits — are which factors played into its surge and whether they’re sustainable.

Harmon sees multiple possibilities. He noted that to make people aware of the show’s return from its long vacation, fans and stars, led by Joel McHale, not only went to the mattresses with social media promotion, but that NBC delivered on-air spots (including placement in the prime territory of reality hit “The Voice”) in an unprecedented fashion.

“I certainly felt that way last week and for the first time in three years,” Harmon told Variety, “I hope it wasn’t a fad for (NBC Entertainment topper Bob Greenblatt) or a phase. I e-mailed him and said, ‘This network has always been patient with the show, but last week felt like NBC was proud of us.’

“If those two things are the two specific things that brought the show back, then we’re in good shape, because the fans can keep doing that and NBC can keep putting ads on the air. If it was just the halo effect of everyone tuning in (because of the drama surrounding the show’s uncertainty), that scares me, because that means next week, that’s not repeatable.”

Another short-term/long-term issue for “Community” is the looming presence of CBS’ dominant mainstream hit “The Big Bang Theory” as competition; it’s on a brief vacation last week and this week to make way for college basketball’s NCAA tournament.

Though a multicam sitcom with a more traditional structure, “Big Bang” shares with “Community” characters in a college-set world, an unadulterated fondness for pop culture and an appeal for young-male demos. Harmon said that research has shown that “Big Bang” and “Community” have a “huge overlap” in audience, in the neighborhood of 30%.

Consequently, many have long speculated NBC has tamped the ratings potential of “Community” by leaving it in the shadow of “Big Bang,” which moved from Mondays to Thursdays before the 2010-11 season. While last week’s numbers seemed to validate that theory, Harmon said it wasn’t his primary concern.

“That’s so far beyond my jurisdiction,” Harmon said. “I’m so honored to be at 8 o’clock because it is the Vietnam of that night — it’s the front line — so it’s an honor when the general says to you, ‘I need you out there.’ I would never crave anything more. The only bummer is when we come home all covered in blood, that they think that’s our fault. As long as they just go, ‘Good job, soldier — I’m glad that you’re covered in blood,’ I would just thank them forever.”

Twelve episodes remain for “Community” this season — double its usual amount at this time of year — so there is plenty of time remaining for NBC to evaluate the series. But on a network that has struggled to gain any ratings traction among scripted series in recent years, the notion that it would cancel a series with the potential to surprise and grow seems more unlikely.

Harmon said that when “Community” went on hiatus and a renewal seemed less probable, he reached “a place where I was comfortable being done with it emotionally.” But at least for a moment, the most recent ratings changed all that.

“There have been national tragedies on the news that I have reacted less personally to,” Harmon said with amusement. “Looking at my cellphone (Friday morning), I was sitting up in bed, and my girlfriend woke up because I was going, ‘Oh my God! Oh my God!’ The third time, she said, ‘What? What?’ because she thought the White House was under attack.

“I said, ‘This is the only time I get to tell you this, so let me take my time. We got a 2.2 last night.'”