> Perhaps this was a rare case where the odds would have been against non
> helmet survival,
It probably was a pretty rare case. There's been a fair amount of British research into this topic, most recently the study discussed in this article: http://www.cambridge-news.co.uk/Home/Cycle-helmets-useless-in-serious-accidents-claims-report-08032012.htm
That doesn't go into much depth on the findings, but the studies usually say that the overwhelming majority of cycling fatalities occur when a cyclist gets dragged under the wheels of a left-turning truck, for which you'd pretty much need full body armour to survive, if even that. I'm not sure if those findings are applicable outside Britain and Ireland (of course if they were it would be a right-turning truck), but I can't think offhand of any reason why they wouldn't be.