North Carolina Coach Roy Williams talks to his players during a timeout Friday night. The Tar Heels lost, 93-83, to Duke in an ACC semifinal at Barclays Center in New York. (Julie Jacobson/Associated Press)

It seems almost unfair to talk about the future when the present is so compelling, when this month either Duke or North Carolina — or both — could make another march through March to another Final Four. But even as Mike Krzyzewski implored his team from one bench Friday night at Barclays Center and Roy Williams removed his specs to enter the huddle and address his team near the other bench, old players from each program could gather with each other and talk about what old players talk about: Who’s next?

“Even when I was in school, that was a topic going on,” said Shelden Williams, who grabbed the last of his rebounds for Krzyzewski’s Blue Devils in 2006.

Antawn Jamison, a downright Tar Heels legend, now does some commentary on Los Angeles Lakers games, where Hall of Famer and Carolina hero James Worthy is occasionally his partner.

“We talk about it just about every time,” Jamison said. “ ‘How long do you think Coach Williams got? Who’s going to be next?’ ”

This was the discussion, even in the midst of the ACC tournament, even leading up to the Blue Devils’ enthralling and surprising comeback win, one in which they turned a 13-point deficit into a 93-83 victory in the semifinals. The coaches define the programs. The coaches know the history. The coaches know what happened.

Duke Coach Mike Krzyzewski reacts to a play in Friday night’s game — the 30th time he has faced off against North Carolina Coach Roy Williams. (Al Bello/Getty Images)

“It was a big-time game for a while,” Roy Williams said. “And then it got so it was not such a big-time game.”

So much about each of these teams could be fascinating over the next few weeks: Whether Harry Giles, Duke’s gifted freshman whose season was derailed by knee surgery in October, could contribute as he did Friday (four blocks, seven boards in 15 minutes) just as his classmate, lithe Jayson Tatum, could develop into the top pick in the NBA draft. Whether North Carolina’s talented big men, Kennedy Meeks and Isaiah Hicks, can produce consistently, giving the Tar Heels complements to ACC player of the year Justin Jackson and point guard Joel Berry II, whose fourth foul served as the pivotal point Friday night.

And yet we’re left with so many unavoidable realities about these two programs.

Krzyzewski turned 70 in February. Williams turns 67 in August. Krzyzewski entered the Hall of Fame in 2006. Williams entered the following year. Krzyzewski is in his 42nd year as a head coach, his 37th at Duke. Williams coached at Kansas for 15 years and is completing his 14th season at his alma mater. Krzyzewski has won five national titles, an NCAA record (non-Wooden division). Williams has won two since returning to Carolina in 2003. Krzyzewski missed a month with a back problem earlier this season. It has long become a parlor game in Chapel Hill to speculate how worn Williams looks, particularly after a loss.

“Right now, it’s best for me to stay away from my players,” Williams said after Friday’s defeat. “I’m ready to jump off a building or something like that.”

They are giants and fixtures, stewards of a sport in which the players pass through but the coaches are the constants. And even as this ACC tournament produced a compelling matchup between the two of them — the 30th time they have faced each other, just the second in the ACC tournament — people are wondering not when these coaches will jump off a building but when they will walk away.

“You look at North Carolina, you look at Duke — I don’t know how long Coach Williams or Coach K is going to be able to go,” Jamison said. “That’s going to be interesting. It’s going to be interesting to see if they stay within the family.”

Stop right there. That idea of “family” is bandied about both programs. Jamison’s blood runs as light blue as his brethren’s, and he knows the problems handing the family business over to a son can bring. He was there on that October day in 1997 when Dean Smith, supposed to be entering his 37th year at Carolina, walked in and told his team he had always known he would step away if he couldn’t give his players 100 percent. He could no longer assure them that he could.

After three years with Bill Guthridge, Smith’s assistant of three decades, at the helm came the period observers of both programs dread: Williams, the obvious choice, said he couldn’t divorce himself from the Jayhawks. Carolina worked through Smith’s coaching tree, and the wheel somehow landed on Matt Doherty, a teammate of Michael Jordan and Worthy on Smith’s 1982 NCAA title team who had served as Williams’s assistant and then the head coach at Notre Dame for a season.

Doherty’s reign is not remembered fondly in Chapel Hill. “We tried a young guy and so forth” is how Jamison glossed over it Friday. That three-year ride ended in Doherty’s dismissal and is precisely what alumni on both ends of Route 15-501 fear could be next.

So those discussions become circular. Duke has former players Chris Collins getting Northwestern into the NCAA tournament for the first time ever, Steve Wojciechowski leading Marquette, Bobby Hurley heading Arizona State and Jeff Capel, the former coach at VCU and Oklahoma, now back assisting Krzyzewski. Carolina has — not as many.

“We don’t have that deep coaching tree like we used to have,” Jamison said.

And so they talk about the candidates. And the difficulty of being the next guy.

“You’re talking about somebody’s who’s iconic,” Shelden Williams said. “It’s going to be some big shoes to fill. Maybe a guy like ‘Cape’ who’s actually played and actually coached at a high level. But it’s still going to be tough, whoever it is.”

Who it is right now: Hall of Famers, coaching their teams. Krzyzewski drew on his past when, after a vicious Tatum dunk pulled Duke within 61-50, he called a timeout to tell his team: Let’s make a run. The next exchange: Carolina missed, and then Luke Kenard nailed a three-pointer and was fouled.

From there, Duke rolled.

“Whatever good decision or bad decision, I’m not afraid to make a decision,” Krzyzewski said. Eventually, each of these schools will have a momentous decision to make, decisions that will affect the future of two of the sport’s flagship programs. There’s no guarantee the names Duke and North Carolina carry success into the future on their own.

But for now, we have March and moments like Friday night, when the clock ran down and Roy Williams went to shake Mike Krzyzewski’s hand. Till they meet again.

For more by Barry Svrluga, visit washingtonpost.com/svrluga.