Horner has done an excellent job turning Red Bull into a winning machine, which last year produced the most dominant season in F1 history, taking victories in 21 of the 22 races among an avalanche of new records.
But to suggest he was singlehandedly responsible for their success would be to misunderstand Red Bull.
The team’s main secret is chief technical officer Adrian Newey, to many minds the greatest design engineer F1 has ever seen.
The 65-year-old is a unique talent with a vision for aerodynamics – the key science behind success in F1 – like no-one else in the sport’s history.
Red Bull have managed to set up a structure around Newey that maximises his creative talents while removing from him the areas in which he is either less interested or less skilled. Before that, he was famously bogged down by the complicated ‘matrix’ management structure imposed on him at his former team McLaren.
Success in F1 is never down to one person, but if you were forced to pick a single name as the decisive influence at Red Bull, it would without any question be Newey.
It is not a given that Newey would be discomforted by Horner’s departure. They may share an extreme level of competitiveness but they are very different characters, Newey’s diffident nature contrasting with Horner’s front-foot aggression.
Nevertheless, the two are closely connected. It was former F1 driver David Coulthard who convinced Horner that Newey was the key to success when he joined Red Bull from McLaren for their debut season 19 years ago.
But once Coulthard had convinced Horner of the wisdom of the plan, Horner went all in and built the team around Newey, who was poached from McLaren on an initial salary of $10m.
There have been occasional frictions, including in the last year, when an interview Horner gave to a German publication in which he seemed to play down Newey’s influence was said to be met internally with a fast, detailed kick-back from Newey.
But by and large they have made a strong team and if Horner leaves, the vultures in F1 will be circling.
Newey has come close to joining Ferrari at least twice, only to get cold feet at the key moment.
Ferrari might see the drama inside Red Bull as an opportunity to have another go at luring the chief technical officer.
Although the fact that many people in F1 believe – without proof – that Red Bull’s technical director Pierre Wache, effectively Newey’s number two, is already on his way to Italy in the not-too-distant future may complicate matters.