There was a virtually identical incident in 1984 or 85 with a Republic (ex North Central) Convair 580; went into a snowbank on landing and shed a blade that penetrated the cabin and killed a passenger.
As a non-engineer, I'm always amazed that the blades stay attached at all. I assume that the blades on the Q400 are composites; would that have any implications for their sturdiness in this scenario?