After another Spurs exit, is this it for Duncan and Ginobili?

There is a certain comfort one takes in seeing the professional athletes of their youth continue to play, year after year. Yet it doesn't last forever. The San Antonio Spurs' longtime axis of Tim Duncan and Manu Ginobili just completed their 19th and 14th NBA seasons, respectively, and a rite of spring the past years begins anew.

Is this it for the pair of them? Or one of them?

The Spurs' elimination Thursday at the hands of the Oklahoma City Thunder probably comes as more of a sleeper surprise than a true shocker, but the end result brings us back to the same uncertainty San Antonio fans faced last spring - with both players a year older.

Last year, both Duncan and Ginobili announced they would return in July, two months after their first-round playoff exit. Both players can be expected to take time this spring to think about the future and decide accordingly, but the writing may now be on the wall.

Related: Duncan says 'I'll get to that after I get out of here' regarding future

In addition to the model franchise he plays for, Duncan's effectiveness has benefited over the past four seasons by a gradual reduction in minutes. As the Spurs seamlessly morphed over time from his team to a squad highlighted by Tony Parker and then Kawhi Leonard, the Big Fundamental's game stayed, well, fundamental.

Duncan led the NBA this season in defensive box plus-minus, and ranked second in ESPN's defensive real plus-minus. However, reality seemed to appear in four of six games against Oklahoma City. The 40-year-old was frequently rendered a non-factor by Thunder bigs Steven Adams and Enes Kanter, two players who were 4 and 5 years old, respectively, when Duncan entered the league.

That's sports, and that's life. The question for Duncan now will be whether or not he wants to risk further decline in front of millions. It's long forgotten now, but the careers of fellow NBA big men legends Hakeem Olajuwon and Patrick Ewing ended almost embarrassingly with the Toronto Raptors and Orlando Magic. The difference now is, there is an entire social media cottage industry dedicated to picking apart the minutiae of every single individual performance, every night in the NBA.

That is in no way meant to be a bet against Duncan: The only other big man to ever play near his level at his age was Kareem Abdul-Jabbar, who averaged 10 points a game on a Finals team at age 42.

Related: 3 reasons why Duncan, not Kobe, is his generation's best

Duncan has a player option for next season at $6.4 million, and one more year would make a nice, round 20 in the NBA. Heck, his one-time rival Kevin Garnett is expected to be back for a 22nd season. Yet the Virgin Islands native keeps things close to the vest, and most reasoned speculation on his future tends to come from the only pro coach he's ever had, Gregg Popovich.

It was Pop who last year suggested that Duncan would "go for another one."

As in one more season, which meant this one. Then again, Popovich has also plainly put it that the Spurs' aging core in general should always come back, because the "paycheck is good."

For Ginobili, all signs have pointed for a while to this being his NBA swan song. Before last season ended, he told an Argentine newspaper that he wouldn't play beyond 2016. After he turns 39 in July, he's expected to suit up for his native country in the Olympics, which at casual glance could be viewed as perfect punctuation to his basketball career.

Ginobili, like Duncan, also has a player option with the Spurs for next season. Their retirement decisions will be independent, Duncan stressed back in March.

"We're going to make those decisions individually," he said. "Not as a group."

However those personal choices shake out, one day it will be difficult not to remember these Spurs as a group.