In "reality", the "probability" that the LHC will destroy the Earth is either 0 or 1 - either it ends up destroying the Earth or it doesn't - and in fact we know it turned out to be 0.

That doesn't seem to be the case when considering quantum mechanics. If, since the LHC was run, we had counterfactually accrued evidence that a significant proportion of those Many Worlds were destroyed then it would be rather confusing to say that the probability turned out to be 0. This can mostly be avoided by being particularly precise about what we are assigning probabilities to. But once we are taking care to be precise it is clear that the thing that there was 'ignorance' about and the thing that we know now to be 0 are not the same thing. (ie. An omniscient being would possibly not have assigned 0 prior to the event.)