If you're a scientist that subscribes to the many worlds theorem, does that mean you do not accept wave particle duality? Seeing as MW postulates that the wave or particle form has always existed that way in your world (If I understood it correctly)
No, there is no logical dependence on the two. Recall that particle wave duality existed long before the Copenhagen interpretation of QM. Relative to that interpretation the wave and the particle acquire specific meaning but they existence of duality is not dependent on, nor does it require, the Copenhagen view of QM. Particles and Waves were two competing paradigms for describing phenomena that go way back. I say competing since we usually say, based on experience, that something is either a particle or a wave. In fact the "things" to which we attribute these behaviors have proven us wrong. Each is an abstraction based on our experiences. Duality means that the "things" we play with can behave in both ways and there was not reason to choose one paradigm over the other. Now the two views are seen as complementary rather than competing.