This is all wrong, and plain blatant implicit assumptions.
First of all, atoms are NOT observable, in a visible sense anyway. Atoms are a construct we are introduced to in the most basic introductory science courses. What IS visible to us isn't even the direct reception from atoms... ..technically, We do not "observe" photons, either!! what we perceive and recognize as the real physical world is radically and categorically different than the physical input. Photons illicit a series of neurological activation states which yield the percept of a complete object, color, good continuation, all of the gestalt grouping principles of perception, and all other cognitions related to the input that reasult from observing atomic input.
What you ARE doing here, is correlating the construct of the atom which what you see in the real world, but they are not the same thing.
An atom is not a thing in the same sense that an apple is a thing ~ an atom is invisible to us, the apple is not. an atom is, however, observable to us, but again, not in the same way the apple is observable to us.
You are going to have to explain the fundamentals of observations then. We don't directly observe an apple, usually just the electromagnetic effects it has on us. Same with atoms. Since then we have gone on to observe the strong, weak, and gravitational effects it has on us as well.
Both are merely constructs in the sense you give. Atoms are just invisible (to the human eye), apples are visible. Through many experiments, followed by the rest of the scientific method, we have come to observe atoms as we have apples. We just do so less often.
I repeat, if one cannot observe something, it is illogical to state it exists or does not exist. We observe the effects of every particle in the universe on our bodies at this very moment. Not even with a delay caused by c being the only universal constant, as the 'entanglement' effect has shown.
The only assumption I'm making is that your example individual has no confidence in the supernatural. If someone does not have confidence in the supernatural, they must only consider the physical, and in such case the "mind" is fully dependent on the "brain" to function.
You could perhaps consider the brain to the hardware and the mind to be software - if the hardware is damaged the software is adversely affected, much like brain damage. If the hardware is destroyed (or decays to the point of uselessness) the software ceases to function. And the software certainly did not exist before the hardware existed. When looking at a computer, it isn't a stretch to say the software only exists when it exists, couldn't possibly perform/save anything before it existed, or after it ceases to exist, so why would a "meat computer" follow special unobservable rules otherwise?
Okay, first of all, define 'supernatural'. By my definition, if say magic exists, it is natural. Anything observed is part of the laws of nature, if magic is observed, it is part of the laws of nature.
Second, I never said the brain follows special rules. The same can be said of any computer or object, regardless of whether they possess the capabilities for qualitive experience or not. In a few googelplex years, specific computers will be back too, who's to say?
You're also falsely applying the mind to the brain. What if our thoughts are merely a particular formation of electrical impulses? Why then, would destruction of the brain limit that? Certainly effect it, but not so harshly as to stop it from occurring elsewhere, or to stop it changing beyond recognition.
I'm not stating any of these examples with the force of evidence, merely attempting to show that they possess the same amount of evidence as the theories you have claimed, thus far.