I can't speak for the others, but sadly I wasn't there... been down with the flu but still had to attend an outside obligation... *miserable*
However, since I was kind of expecting this, I did go to another shards' event. So I know what happened (assuming they're all the same, which I think they are). Here's what happened! Basically, Casca confronted Dawn and demanded to get the Ruby Gem that she took when we all went to kill the Shadowlords last week. Dawn smashed it, and Casca died. I assume he was like a puppet, and the last remaining remnant of the Shadowlords' will was to acquire the gem: when that was hopeless, Casca had nothing left to drive him. So he died!
And that's why Casca is having a dirt nap right now *grins*
*goes to fetch herself some lemon ginger tea*