Yeah people need to calm the hell down. It's even worse on the Avengers forum.
Look folks this was a tease, and the scene blacked out. We don't know the context, and we don't know what happens after. I seriously doubt this is going to be Empire strikes back where Thor get's an artificial hand at the end, especially with Portman in a lead roll.
The scene blacks out from all the descriptions, without having seen the footage, the description is that Thor call Mjolnir, and then Loki's sword comes down on his hand and the scene blacks out. We don't know any more than that.
I'm guessing this is the scene where Malekith has Jane, and Thor is on his knees crying "Nooo!" from the teaser.
If there's one thing I've learned about trailer footage over the years, is never trust what they show you. I specifically remember Star Trek 6, the trailer showed Kirk being vaporized by a phaser, and this started all kinds of speculation that Kirk was going to die, well that didn't happen (in that movie anyway).
But however you come down on this, this movie sounds absolutely bad ass!