So, question - do we believe Norman is really dead?
By that I mean, imagine a final scene like this:
The deputies carry Norman's body out of the house, followed by Dyan. He sits down on the steps. The sheriff walks up to him and says, "I'm sorry. I can't imagine having to kill your brother. Maybe it's... (pauses) Well anyway, I'm sorry." She turns and follows her deputies down to the vehicles. The camera slowly zooms in on Dylan's face. After a moment he says, softly, in a Norman-like voice, "Yes, it's too bad Dylan had to die."