Will there be further investigations? I believe the RAIB digest is final, and they said that they were unable to determine whether the driver's fasting was a factor.
I would presume the TOC will have investigated, and given the time elapsed I suspect some form of conclusion would probably been reached now.
Were it to happen where I am, the driver would be interviewed initially, and then once the initial investigation is completed there would be a follow-up interview during which some form of action plan would be mutually agreed. This could include additional training or mentoring, but equally the driver may agree to make changes to their daily routine / lifestyle.
The latter can't be forced, but if the driver starts developing a history then the disciplinary route will come into play sooner or later. One still has to rely to some extent on the individual choosing to co-operate with the process, although monitoring helps enforce compliance.
Another option is of course the driver could decide that the vocation is no longer for them, and they could be supported into finding alternative roles within the company.
If I've read correctly it appears the driver offered the fasting as a potential contributory factor, one would suspect in response to questioning at interview. Factors such as health, diet and meals are certainly probed where I am, so somewhere along the line he's bound to have been asked something like "When was your last meal", which will likely have been followed up with "Did you feel well nourished?", and "Do you feel this may have been a factor?".