Ian,
Please correct me if I'm wrong, but wouldn't (non-reductive) materialists and epiphenomenalists just say that the original person would be one realisation of a certain pattern, and that the dupiclate would be another realisation of the same pattern.
Let's assume that (non-reductive) materialists and epiphenomenalists accept that a brain can be aware of its own existence. Now, that would involve a notion that you're this specific brain and not any other structurally and functionally identical brain. Assuming that a 'conscious brain' has a natural interest of surviving as this particular brain, it does make an important difference whether you're going to survive yourself or whether someone else with the identical psychological structure and content is going to survive.
Have I missed something? If so, please tell me what it is.
Titus