It's tough mate. Been in the same boat, although it was a motorcyclist and he was breathing, but he was a mess... after they shut the road and worked on him for an hour, they called it a day.
Well done for stepping in. Give yourself some time and rest mate, take the positives out of it. You will probably be a little up and down cos of the shock, but remember you did all you could and that's as much as anyone could ask.
BFTA/NSRA County Coach
CSFTA Chairman/BFTA Rep