The Yankees’ stars aren’t as young as they used to be, but that doesn’t mean New York is no longer a threat to contend. (HANS DERYK/REUTERS)

This was the winter the New York Yankees were forced to confront their baseball mortality. No, not any sort of imminent demise — because 2011 shapes up just fine for the Yankees, despite claims to the contrary — but the long-term viability of this dynasty they have built, one that has made 15 playoff appearances and won five World Series titles since a certain baby-faced shortstop showed up in the Bronx in 1995.

Think about all that befell the Yankees this winter, starting with the disintegration of the so-called “Core Four” — not only Andy Pettitte’s retirement, but also Jorge Posada’s forced move to designated hitter, Derek Jeter’s semi-contentious contract negotiation, Mariano Rivera’s reported flirtation with the Boston Red Sox.

Then, add the spurning of the Yankees by free agent ace Cliff Lee, the first superstar the Yankees targeted but failed to nab since Albert Belle in 1998. And the implication made by current ace CC Sabathia that he might exercise a contractual opt-out clause after the 2011 season. And the split, acknowledged publicly, between ownership and the front office over the signing of reliever Rafael Soriano to a three-year deal.

Suddenly, the Yankees were confronting big questions: Where’s it all heading? How long can the good times last? How much do Jeter, Rivera and Posada have left, and who will replace them as the soul of the team? And most of all: Will the Yankees always be contenders just because they’re the Yankees?

“We’re gonna be in it every year,” Yankees general partner Hank Steinbrenner boasted earlier this spring, sounding almost as if he were trying to convince himself. “Every single year. You can’t say that about any other team, except maybe the Red Sox. But they weren’t in it last year. . . . The only team you can be assured, as long as we own them, is going to be in it every single year is going to be us. We’re going to be a major contender to win the championship every year.”

But is it that simple? Do the Yankees’ vast resources and perennially league-highest payroll guarantee not only immediate success — but sustained, dynastic success?

“No, you can’t assume anything in this game,” said first baseman Mark Teixeira. “But we’re still the Yankees. The last 15 years, we’ve been pretty darn good. And I don’t see any reason why we won’t continue to be good.”

It wasn’t all that long ago that the Yankees were like any other team, needing everything to go right for them in order to contend, and mostly coming up short. There were 12 straight seasons without a playoff appearance from 1982 to '93, six straight finishes in fourth place or worse 1987-92, four straight losing seasons 1989-92.

Younger Yankees fans have no memory of those dark ages. To them, that aberrational stumble in 2008 — a third-place finish that remains the only season without a playoff appearance in the Jeter/Rivera/Posada era — was enough to make them think the sky was falling.

But here is what the next five or so years hold for the Yankees: Posada, Rivera and Jeter (most likely in that order) will fade to black. Alex Rodriguez, now 35 years old with seven years and $174 million left on his contract, will age into a DH-only player, and Teixeira, 30, will start down that path. Robinson Cano, who recently hired Scott Boras as his agent, will start clamoring about wanting a Jeter-like contract. And Sabathia, a perennial Cy Young candidate, will either opt out of his contract or extort the Yankees into giving him a risky, long-term extension.

More and more, the Yankees’ long-term future appears tied to such young stars-on-the-rise as catcher Jesus Montero and 19-year-old lefty Manny Banuelos. And the trick for the Yankees, as always, will be to resist the old urge to trade those pieces for more high-priced veterans.

“Hopefully we’ve found a core group that’s going to stick together,” said veteran right fielder Nick Swisher. “This organization is capable of producing young players, or going out and getting veterans. It’s good to have both options.”

If the long-term future of the Yankees is murky, the short-term future is not quite as dire as many are making it out to be.

True, the Red Sox, having added slugger Adrian Gonzalez and speedster Carl Crawford this winter, have the look of a World Series contender. But the Yankees will essentially be fielding the same team (minus Pettitte) that won 95 games and scored the most runs in the majors — only with a better bullpen, fortified by the signing of Soriano, this time around.

“Everyone seemed to focus on who we didn’t get” this winter, said veteran pitcher A.J. Burnett, referring obliquely to Lee. “But I see a ton of great arms in here, a ton of talent. There’s a lot of confidence [among] this pitching staff. If we stay healthy, we’re going to produce.”

Much has been made of the thinness of the back end of the Yankees’ rotation, but the collection of retreads (Bartolo Colon, Freddy Garcia, Sergio Mitre) and youngsters (Ivan Nova) vying for the last two spots had combined for a 1.13 ERA this spring entering Friday.

And as always, the critical thing to remember about the Yankees is this: Whatever their rotation looks like on April 1, it almost certainly won’t look the same on August 1. All that money Lee turned down this winter? It’s still available, and the Yankees will be in on every ace, innings-eater or gun-for-hire on this summer’s trade market.

They’re still the Yankees, as Teixeira says. And at least for the time being, they’re not going away.