Until there's evidence otherwise, I would assume that they can be killed in much the same way any other living thing can be killed.

[He glances at Boone's image on the communicator only briefly, his attention transfixed on the Prop. It's keeping very still now, and Narvin is staring at it with predatory focus. He wonders if he can stalk up upon it slowly and pounce.]

I just haven't been able to put that to the test yet.