From being the Premier League's finest defender last season, this year we're talking about how his leadership is crucial to Chelsea in the club's attempts to rebuild from the wreckage of 2015/16.
That process has barely started, which is why Terry being offered a new contract for next season is imperative. Outside of him, the connection between the past and what Chelsea have come to represent this past decade or so is lost.
Chelsea haven't done a good enough job of regenerating and maintaining that winning culture—of which the 35-year-old is the embodiment—throughout the dressing room.
Everything once revolved around the spine of Petr Cech, Terry, Frank Lampard and Didier Drogba. As age dictated that be dismantled, those who have been signed as part of the restructuring haven't lived up to expectation.
Added to that, Chelsea have been guilty of enjoying too much of a good thing. The club became embarrassed almost by what got them this far in the Roman Abramovich era and went too far in their move away from it.
For a team funded by a multibillionaire owner, Chelsea haven't always appeared as one. The football has been based more around endeavour and organisation, whereas the masses have long expected a touch more effervescence to justify the massive outlay on players.
When the trophies were rolling in, few cared at Stamford Bridge. Now that success hasn't be so consistent, however, the club has tried to move away from that culture and implement a style more appealing to the neutral.
That's been a mistake for multiple reasons.
Above all else, that transition was made too late in the team's cycle of the Cech-Terry-Lampard-Drogba era. With a succession of managers, it hasn't been handled properly, either.
Ultimately, that's made a major contribution to the problems we're seeing now.
From being a well-oiled machine, Chelsea have become a team at odds with itself. From putting an emphasis on diminutive attacking types, the focus defensively has always been on juggernaut stoppers to bash opposition attackers into submission.
It may make them defensively sound, but going forward it has the opposite effect. Chelsea's big struggle as a collective has long been what they produce in attack.
It's one thing having all that attacking flair, but if you're not getting the ball forward efficiently enough to those champagne players, it's always going to be difficult to break teams down.
Which is why Terry actually hinders this team. Just ask Andre Villas-Boas.
It's almost five years since the Portuguese manager returned to Stamford Bridge proudly declaring that he came with a mandate to revitalise a squad that was ageing.
He was supposed to be the future. Chelsea were building around a manager.
A former member of the backroom staff under Jose Mourinho, Villas-Boas had flown the nest of his mentor to carve out his own career. He had impressed by winning titles with Porto, and Chelsea wanted the same in west London.
He was just 33 when he replaced Carlo Ancelotti, and his ideas were as fresh-faced as he was.
It was Villas-Boas who signed Juan Mata, for instance, giving Chelsea the sort of attacker they hadn't seen since Gianfranco Zola.
We could see where the manager was attempting to take things, but his problem was the old guard. Drogba, Lampard and Terry remained, and they didn't quite fit his system or style of play.
Given that Chelsea would go on to win the UEFA Champions League that season in Villas-Boas' absence—he was sacked just eight months into his reign—history tells us the club were right to remove him from his post when they did.
Looking at where Chelsea find themselves now—still reeling from this prolonged transitional period in which it's not clear where the club is heading and what their philosophy actually is—perhaps events since then tell us it was actually wrong.
A sign of how difficult Villas-Boas would find his spell at Chelsea came in late October 2011 when Arsenal came away from Stamford Bridge with a 5-3 victory.
It wasn't the scoreline that was alarming, but more the way Terry had come unstuck against Robin van Persie as he attempted to recover from a poor back pass by John Obi Mikel.
The score was 3-3 at the time. Mikel's pass isolated Terry close to the halfway line, and knowing Van Persie would be hot on his heels, the Chelsea captain panicked. So much so that his legs couldn't move quickly enough for his body and the defender crashed to the ground.
Van Persie ran through on goal to round Cech and score into an empty net to put Arsenal in front with just five minutes remaining. The Dutchman completed his hat-trick in that game in the 90th minute.
In some ways, that was the beginning of the end for Villas-Boas. It was just a third defeat in 15 games, but it was the sight of Terry being left in Van Persie's wake that was so alarming.
It was clear the manager's high defensive line that we hear so much about these days wasn't going to work with his captain in the team.
Terry has never been mobile or quick enough to play that way. Because he was John Terry, Villa-Boas had no choice but to persevere.
Because he's John Terry—the captain, leader, legend of Stamford Bridge—Chelsea have had to, also.
Of course, it's not a bad compromise to make. Chelsea have to play a certain way with Terry in the team, but look at what that has delivered the club in the 17 years since he made his debut.
Terry rightly sits among Chelsea's greatest names. He's the club's most successful captain and will finish his career just shy of Ron Harris' appearance record for the club.
His one-club career has been unique in the modern game, as has the power he has exerted in the halls of Stamford Bridge.
When he does eventually depart, however, Chelsea can finally play catch-up in the modern game.
Since Terry lifted his first Premier League title in 2005, the landscape of football has changed significantly. Abramovich has recognised that with the way he has desired the club move forward.
Because of legends like Terry, it's caused the club to flinch at crucial moments, though. They've flirted with the idea of changing the club's philosophy. They've even made the moves in the transfer market to do just that only to pull out at the last minute.
It's left Chelsea completely unbalanced.
Signing Mata, Eden Hazard, Oscar and others told us they wanted to move in a different direction, but then placating stars like Terry has subsequently held them back.
Terry's been great—he is great. When he's not around anymore, maybe Chelsea will be again, too.