CHICAGO -- The ball bounced off the left upright, kicked the crossbar and trickled to the ground, altering the trajectory of two NFL franchises.

Had Cody Parkey's 43-yard field goal attempt sailed through the uprights Sunday night, the Chicago Bears would be readying this week for the divisional playoff round. The Philadelphia Eagles, on the other hand, would have entered the offseason prepared to bid farewell to backup quarterback Nick Foles, a likely free agent.

The Eagles' 16-15 victory, however, reinforced that their looming decision is more fraught and less obvious than it seems. There is no reason for them to give up on starter Carson Wentz, who suffered season-ending injuries in 2017 and 2018. But in Foles they have a proven winner whose performance over the past two seasons has reached a level of historic proportions that cannot be ignored.

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His fourth-down touchdown throw to receiver Golden Tate on Sunday night might have been forgotten -- unfairly -- if Parkey had converted. Instead, it made Foles the winningest quarterback in Eagles history (by percentage, .676). He is one of five quarterbacks in the NFL's modern era to win five consecutive games as an underdog, according to the Elias Sports Bureau research. Yet we all continue to underestimate and misunderstand Foles when he starts for the Eagles.

"He lets people talk and do what they're going to do," Eagles defensive end Brandon Graham said. "But he doesn't get caught up in the hoorah. If stuff happens, it happens. If not, he's going to live to another day. I love his mentality. He never wavers."

There was a time when Foles' performance with the Eagles seemed a perfect, if short-term, storm. That stage has passed. How many big games do the Eagles need to win with Foles before the conversation becomes sticky?

I think we're getting there -- if we aren't there already. Special things happen when Foles puts on the green and white. There has never been a quarterback in NFL history who has won a playoff game in consecutive seasons despite starting five or fewer games in each of those regular seasons, according to Elias research. In other words, backup quarterbacks never accomplish what Foles has.

So at the very least, the Eagles would be parting ways with a playoff-tested quarterback who has played at an unprecedented level when pressed into duty for two consecutive seasons. Is that smart team-building?

The objective answer is no, but reality might leave the Eagles with an imperfect choice. They can control Wentz's rookie contract for two more seasons. Foles, however, has a rare mutual option in his contract for 2019, meaning the Eagles can keep him if they want to pay out a $20 million salary. And even if they do, Foles can void the option by returning $2 million of his original signing bonus.

It's difficult to imagine the Eagles giving up on Wentz or wanting a $20 million backup quarterback. Nor does it seem likely that Foles would return just to sit when he almost certainly would have multiple options to start elsewhere. But he already has learned the fallacy of greener grass; he nearly retired after a failed run as a starter for the St. Louis Rams in 2015. Foles might be the rare player for whom a backup job in the right place is preferable to a starting role in a bad environment.

Foles sounded a bit wistful Sunday night, admitting he has been taking a moment "to reflect" and realize how good he has it with the Eagles.

"I realize that I'm blessed to be able to wear this jersey at least one more week," he said, "and I get to play with these guys one more week."

Foles had nothing close to a perfect game Sunday night. He threw two first-half interceptions before the Eagles limped into halftime with only three points. But he turned on the magic after the Eagles regained possession when trailing 15-10 with 4:48 remaining.

He completed 6 of 9 passes for 59 of the Eagles' 60 yards on the drive. Facing fourth down at the Bears' 2-yard line with 56 seconds left, Foles called timeout. On the sideline, he suggested to coach Doug Pederson a sprint-out pass, knowing the Bears were likely to blitz. Pederson agreed, a moment reminiscent of Foles' nomination of "Philly Special" during Super Bowl LII.

Right tackle Lane Johnson was struck once again by how calm Foles appeared in the moment as the quarterback jogged back to the huddle.

"It wasn't 'The Replacements,' where they have a good message there at the end," Johnson said. "It wasn't 'Friday Night Lights,' [where they say], 'Let's go boys, let's go fetch the state championship.' It was, 'Call the play, and let's go see if we can score.'"

Foles found Tate near the pylon and fired a perfect pass.

"We always talk about just staying in the moment," Foles said. "That's been what I've been focusing on, what we've been focusing on."

It will all end at some point. Perhaps it will be next week against the top-seeded New Orleans Saints. Maybe the Eagles will keep it going to the NFC Championship Game. Who knows? Maybe Foles will bring them back to the Super Bowl.

Whenever it does end, and no matter how it happens, how comfortable should the Eagles feel about letting Foles leave? Given Wentz's health history, shouldn't the skill of his backup be a high roster priority? And as for Foles, is leaving the right decision?

Six weeks ago, those questions wouldn't have been difficult to answer. Now they are. NFL teams sometimes allow good players to leave in free agency. It almost never happens with quarterbacks. Foles isn't just a really good backup. He's the guy who has started all of the Eagles' biggest victories in the past two seasons. The chances of finding a comparable replacement are low. Should they let him go? It's a tougher decision than we might have realized.