|Bianchi remains in a critical condition two weeks after|
his Japanese GP accident.
The problem in this accident was the violent and sudden deceleration of Bianchi's head - restrained by the HANS device - which could not be matched by the brain inside the head. Bianchi's brain will have suffered a heavy impact his skull, which is what lead to the widespread brain injury. This is different from the injury suffered by Michael Schumacher, for example, where the injury was caused by an impact to the head causing bleeding inside the cranial cavity.
The HANS device may sound like it's the problem, but actually the restraint is probably the only thing that has allowed Jules to continue fighting for so long. Without the HANS device the outcome would have been far worse. The last driver to die in an F1 car was Ayrton Senna. Whilst a lot of discussion has been had around the suspension arm from Senna's Williams puncturing his helmet and skull it should be remembered that Senna suffered a Basal Skull fracture which would have almost certainly been fatal anyway. Roland Ratzenberger's death was caused by the same injury, as were NASCAR drivers Adam Petty and Dale Earnhardt.
A basilar skull fracture is caused by the sudden deceleration of the shoulders and the continued forward motion of the head and helmet causing the skull/neck to fracture at the point where the spinal cord enters the skull. Whilst not always fatal in normal life, the violence and forces involved in racing accidents mean they usually are.
The HANS device can prevent that stretching of the neck, but in a violent impact like that experienced by Bianchi the organs of the body have so much momentum that they continue moving until they hit something solid - ribs, skull, pelvis, etc.
Had Bianchi been enclosed in his cockpit it's unlikely that the outcome would have been significantly different. The collision with the tractor resulted in his car decelerating significantly harder than a collision with the tyre wall that was behind it and it is this that needs to be the focus of the investigation.
Closed cockpits are not the wrong answer for F1, but to ensure that Bianchi's accident can't happen to somebody else more work needs to be done to ensure that cars leaving the track only impact with barriers that have been designed to soften an impact.