The chief virtue of decoherence and MWI (as I understand it) is that it avoids 'the measurement problem' or the necessity of a natural observer. If you go back far enough in the history of the universe, there were no natural observers.
Well the beauty of the actual system is that you don't need a "natural observer" until you have one. You calculate the time-evolution of the system with non-collapsing wave functions, then you collapse the wave function only when an observer finally shows up to make the observation.
It doesn't matter if the wave functions were waiting billions of years to finally be collapsed, you are not missing anything by not having collapses before you have natural observers.
How many universes "branch off" from a "quantum event", and in how many of them is the cat dead vs alive, and what about non-50/50 scenarios, and please answer so that a physics dummy can maybe kind of understand?
(Is it just 1 with the live cat and 1 with the dead one?)