1 Alvissa: So Dwalin, does this match up with the dwarven idea of the afterlife?
2 Dwalin: Nay. Thu dwarven ufterlife is a big cuvern fuul o' goold 'n' beer 'n' orcs tae kill. {translation: No, the dwarven afterlife is a big cavern full of gold and beer and orcs to kill.}
3 Alvissa: We've got pretty much all of that here.
4 Dwalin: Und noo elves! {translation: And no elves!}
4 Alvissa: Well, except the orcs are technically already dead...

So is it possible to kill someone in the afterlife?

I guess it depends on what sort of afterlife it is.

And if you get killed in the afterlife, do you go to the after-afterlife?

If this immediately brings to your mind an infinite regression of after-after-after-after-...-afterlifes, then you've been reading this comic long enough for it to have affected your mind. :-)