You might have to break Lavinia's spine and gouge out her eyes to really finish the job, but I think this would be pretty total.
I think Shakespeare didn't go further with the violence, or kill her, because he had to deal with the realities of the stage -- you can't just lop limbs off an actor, however much you might want to. And there's also the clear goal of using Lavinia later on in the play, which might explain the decision to mutilate Lavinia in a manner that could be horrifying, visible and easily done with 16th century stage equipment. Otherwise, yes, Shakespeare could have killed her off as easily as Kid whacked Horatio.
I do think that it would have been, uh, interesting for Shakespeare to have blinded Lavinia, but for entirely different reasons.
Justice. As early as the Romans, Justice was depicted as a blind woman. Lavinia's own blinding would have been an excellent reference to this same concept. I can't decide if it was a blindingly silly mistake by Shakespeare not to include this, or a brilliant decision to ignore an obvious reference. Either way, it would have been fun.
