To zero in on the part of this line of questions that's relevant to the above...

1) The vacuum state is orthogonal to any states which represent minds, because no component of a mind is the empty state.

2) Even some mind has some tiny sliver of amplitude of |0> in it somehow, then if you apply the retarded Green function to it to extract how it got into that situation, the result isn't going to look like |0>, so you're violating the assumptions of the hypothetical. At best, it's going to look like converging radiation, i.e. a conventional Boltzmann Brain.

3) IF the conscious being had existed before finishing off the math, then it would still be there afterwards. But when the cancellation comes up, we instead are finding out that we'd been wasting our time considering it because it wasn't there after all.