In a non-MWI interpretation of QM, is being in a "mixed" state a meaningful property for a single particle or "system"? Or is "mixed state" only a property of a population of particles or systems? ( For example, in a non-QM setting, when we speak of "the probability that a person is over 6 ft tall", we have in mind picking individuals at random from a population and measuring their height once rather than picking an individual from a population and measuring his/her height at 100 randomly selected times during the day. )And after decoherence its in a mixed state so superposition isn't really applicable anyway.
That's basically whats going on - after decoherence each element of the mixed state is interpreted as a world.