Watching the QuakeCon demo, there is an instance where a guard is killed when the dragon "snaps" or, rather, bites at it. The guard stumbles back and then slowly collapses. This looked like a very unique animation (think of it as sort of a "struggle" before the imminent death, which would be nice. Something people have complained a lot about with Oblivion, where once you die, ragdoll takes over and you just flop lifelessly to the ground).

Is this an instance of Havok Behavior? Or is this simply a "triggered", scripted animation when a dragon attacks a guard?

Well BGS has stated that they updated the engine quite a bit since F03 but it may be a pre set scripted death anim. Like the NPC's have a number of death anims that work with how they are being attacked/killed. Anyway they are a part of eachother so it's due to both the engine and the anims.

Yea that annoyed me a little in oblivion how it was like "completely full of life- to instant death"

I didn't notice that in the demo I may have to go back and have a look.

Eh I didn't really mind it but it can definitely do good to add some death anims in. Maybe after you make the final blow the NPC could be suspended in a disbelief before falling backwards or maybe depending on area of final strike they could hold their injury taking a few steps back and collapse.

It looks like an actual death animation. Too bad they don't use that too often. (Bandit death by arrow)

I'm all for more death animations. The standard 'fall back' in Oblivion was good funny for about five minutes, then just 'this is ridiculous' funny after that.