I'm not sure it matters to the analysis. Whether we have a Tegmark multiverse, or Everett MWI with some decisions depending on quantum randomness and others classically determined, or whether the multiple worlds are purely subjective fictions created to have a model of Bayesianism; regardless of what you think is a possible reduction of "possibly"; it is still the case that you have to live in the reality which you helped to create by way of your past actions.