There are a few things regarding Button that a lot of people are missing here. First of all the age thing. Let's look at some of the field for next year. Jenson is 34 years of age, turning 35 in January.
Kimi R?ikk?nen - age 35
Felipe Massa - age 33
Fernando Alonso - age 33
Lewis Hamilton - age 29 (turns 30 in January)
Somebody please explain to me how is Jenson Button too old for F1 when he isn't even the oldest driver on the grid ? Fernando Alonso, the supposed savior of McLaren with a multiyear contract is a year younger than Jenson. Even the baby faced Hamilton is about to turn over a new decade. A lot of people seem to mistake Button's massive experience and longevity for old age alone. In my opinion Button's longevity in the sport speaks on his behalf, not against him.
Secondly there's the matter of finances. It's true that Jenson's salary is reportedly around ?10 million higher than Magnussen's. However there is something that Sky F1's Ted Kravitz pointed out that I found very interesting. Without Jenson's efforts espcially in the last few races, McLaren would've finished handily behind Force India in the constructors' championship. This would've translated into a loss of tens of millions in prize money. Jenson effectively earned his salary himself, making the argument about the "price gap" between the two drivers a bit more complicated.
It is quite widely reported that McLaren are still seeking for either a title sponsor or other major sponsors for next year. Supposedly it's also the reason for not confirmingtheir driver lineup yet as they want to announce everything at once. Ron Dennis has been spotted in Denmark trying to win over local businesses which makes sense since it isn't exactly a secret that Ron would prefer the danish Magnussen in the long run. My personal opinion is that it's sligthly more convoluted than that. Ron desperately wants to push his own will and retain the dictatorship like grip on the team he has always had. Having to bend to the will of the board of McLaren (who supposedly prefer Button) would be a huge blow for Dennis's ego and authority.
As far as marketing and sponsorship goes, I am baffled as to why Dennis and McLaren are not fishing for sponsor(s) in Japan ? Button is much more marketable than his young team mate and even more so in Japan. In the land of the rising sun Button is beat in popularity perhaps only by Kimi R?ikk?nen, not least because of his wife Jessica. In addition to his fame and popularity, Button is also familiar with the ways of japanese (working) culture from his BAR-Honda days, which means that he is ready to dive in straight away both from a marketing stand point and with Honda's factory in Japan.
We also know Fernando Alonso would much prefer Button as a team mate due to his experience and capability of developing a car. Alonso believes Button would play a major part in McLaren's push towards the front of the grid. Alonso gets along with Button very well but more importantly he believes the englishman poses little threat to him as a stable mate. The spaniard will not want to repeat the events of 2007 when the wet-behind-the-ears Lewis Hamilton gave him all sorts of hell on and off the track and Fernando might see signs of the same in Magnussen.
I believe that this is actually working against Button. Alonso wants to be a team leader, he wants to call the shots and be in charge of as many things as he can. Rumours say that one of Alonso's conditions to stay at Ferrari beyond 2015 would've been the right to pick his team mate. This didn't go down well with Mattiacci and it would go down even less with Ron Dennis. I don't think for a second Alonso has such a clause his McLaren contract but even the perception of him having influence on the team's driver lineup is something Ron Dennis will absolutely not allow. This takes me back to the point I made earlier: I think Ron Dennis wants to get Magnussen on board for reasons that go beyond racing and finances. It'd be a show of strength for Dennis to get his choice of driver and since he has already had to except the fact that Alonso is coming back, he is sure to fight on this matter twice as hard.
Ron Dennis and McLaren do have the valid concern of saving face with keeping Magnussen, however. He replaced Sergio Perez only after one season with the Woking team and letting another young driver go after a single season would do the team's reputation damage in the sense that they might not seem such an appealing prospect for any driver, let alone young talent. They don't want to seem like the kind of people who will have no faith in you and show you the door at the first sign of trouble. However that ship may have already sailed because their ongoing procrastination over the 2015 lineup has already put them in a bad light amongst the F1 following crowd and possibly some insiders as well. The debacle has been a complete PR-disaster for McLaren and now Ron Dennis and other board members have to choose the lesser evil of two frankly bad decisions. Keeping Magnussen will save face but will leave Button, one of the most loved faces in F1, high and dry without a proper sendoff.
In addition to off the track issues, we still have to take into account the results on the track, even though Eric Boullier has stated that the decision will not be based on race results (alone). It'd be a foolish approach not to consider what the two drivers bring to the table when the lights go out on sunday afternoon. While it is too early to tell what Kevin Magnussen is capable of, we can draw some conclusions from his Formula 3 and Formula 3.5 results as well as the past season of F1. To my eye Magnussen has the potential to be blisterignly fast but he lacks consistency. Going back through his race results he does seem to have the upper hand over his team mates but at the same time he was often found at either end of the race results, never in the middle. Button on the other hand is the model of consistency and has from 2009 onwards either matched or beaten his team mate every single season. His worst loss was in 2010 against Hamilton with 214pts vs. 240pts. Hardly a walkover.
2014 was not even a contest between Button and Magnussen, that much is clear. However writing off Magnussen completely is unfair because he was still racing with a rookie status against someone who can only be considered an elder statesman of F1. The points alone may not be the deciding factor as Boullier put it but how those points were amassed is the key question here. Button, while often lacking in pace, hardly put a foot wrong the whole season when it came to pure race craft. K-Mag on the other hand showed on occasion Maldonado and Grosjean levels of recklesness, often drawing some heated commentary from his fellow racers. This, in my opinion, is perhaps the biggest advantage to choosing Button over Magnussen for 2015. Honda desperately need clean laps, as many as possible and the 2009 world champion is the man to bring in those laps. Next year we will be seeing a lot of fresh blood on the grid with the likes of Felipe Nasr, Max Verstappen and Carlos Sainz Jr. Many have raised concerns wheter or not these young guns are ready to play with the big boys with such little wheel to wheel experience. With the grid being as unpredictable as it will be, I feel it would be wise to stick with drivers who know how to stay out of trouble. Granted Magnussen has shown the raw pace is there but it is very raw indeed. Though looking at Ricciardo and Bottas for instance, maybe it is that all important second year that the Dane needs to make his mark. The question is, are Honda willing to gamble on that.
Looking at the conundrum from all possible perspectives, the logical choice would seem to be Jenson Button to join Fernando Alonso for 2015. If it weren't for the switch to Honda powerplants, I would have to give the nod to Kevin Magnussen. Were McLaren to stick with Mercedes, I wouldn't see a reason not to have Magnussen - he has the potential, has settled into the team and can start to find his way just like so many others before him. After all drivers like Hamilton who shine so brigth during their rookie year are extremely few and far between. Would everything stay the same for next year, I could not make a case from the 2009 world champion even thoug he beat his young team mate to kingdom come this season.
But with the massive rebuilding McLaren have undertaken upon themselves, experience, consistency and proven track record are the essential building blocks for a shot at greatness. Having three drivers' world championships between Alonso and Button are by no means a guarantee to anything but the way Honda have been trumpeting their comeback, there is no room for doubts or unknowns. Unfortunately for the young dane, that is presicely what he represents. Had he given his older team mate a harder push, shown some more flare... things would be different. Even though Ron Dennis has ruled with an iron fist for decades, it's become evident that the time for strong individual leadership in F1 has come to an end. McLaren are a works team now and Dennis has Honda's management to answer to. Honda are going to want results and the only way to get those results is with constant and consistent development. Jenson Button has proven to be capable of just that and is all the things Honda are looking for.