There was a video posted on the Trains Facebook Page of the failure from a distance. You can hear the piston disintegrate and bang around. One of the last sounds I could hear before the engine stopped was what sounded like a hollow tube fall on the ground, which I have a feeling was the cylinder head cover (i've dropped them before, they make that same sound) and the chunk of cylinder head falling off the engine. To me this indicates the piston failed first, the head was just a causality of the bits moving around in the bore before they could stop.
As I posted on Facebook, steam railroading is fun aint it? Sometimes you just end up shocked at the end of the day at how the engine was able to break on you. I've seen a similar failure happen and the aftermath, and the helped with part of the repair work. Its not really a big deal, even getting hollow cast pistons isnt the end of the world (would like to know who is making them, they are the same size as another engine I know). The people who deal with these machines on a daily basis don't do it for the money, we do it for the love of what we do. The guys in Durango are very very good at what they do, they can do things there I can't even dream of at the loop. They can fix her up just fine.