I feel safe saying that nearly everyone reading this will agree that, given sufficient technology, a perfect replica or simulation could be made of the structure and function of a human brain, producing an exact copy of an individual mind including a consciousness. Upon coming into existence, this consciousness will have a separate but baseline-identical subjective experience to the consciousness from which it was copied, as it was at the moment of copying. The original consciousness will continue its own existence/ subjective experience. If the brain containing the original consciousness is destroyed, the consciousness within ceases to be. The existence or non- of a copy is irrelevant to this fact.
With this in mind, I fail to see the attraction of the many transhuman options for extra-meat existence, and I see no meaningful immortality therein, if that's what you came for.
Consciousness is notoriously difficult to define and analyze and I am far from an expert in it's study. I define it as an awareness: the sense organ which perceives the activity of the mind. It is not thought. It is not memory or emotion. It is the thing that experiences or senses these things. Memories will be gained and lost, thoughts and emotions come and go, the sense of self remains even as the self changes. There exists a system of anatomical structures in your brain which, by means of electrochemical activity, produces the experience of consciousness. If a brain injury wiped out major cognitive functions but left those structures involved in the sense of consciousness unharmed, you would, I believe, have the same central awareness of Self as Self, despite perhaps lacking all language or even the ability to form thoughts or understand to world around you. Consciousness, this awareness, is, I believe, the most accurate definition of Self, Me, You. I realize this sort of terminology has the potential to sound like mystical woo. I believe this is due to the twin effects of the inherent difficulty in defining and discussing consciousness, and of our socialization wherein these sorts of discussions are more often than not heard from Buddhists or Sufis, whose philosophical traditions have looked into the matter with greater rigor for a longer time than Western philosophy, and Hippies and Druggies who introduced these traditions to our popular culture. I am not speaking of a magical soul. I am speaking of a central feature of the human experience which is a product of the anatomy and physiology of the brain.
Consider the cryonic head-freeze. Ideally, the scanned dead brain, cloned, remade and restarted (or whatever) will be capable of generating a perfectly functional consciousness, and it will feel as if it is the same consciousness which observes the mind which is, for instance, reading these words; but it will not be. The consciousness which is experiencing awareness of the mind which is reading these words will no longer exist. To disagree with this statement is to say that a scanned living brain, cloned, remade and started will contain the exact same consciousness, not similar, the exact same thing itself, that simultaneously exists in the still-living original. If consciousness has an anatomical location, and therefore is tied to matter, then it would follow that this matter here is the exact matter as that separate matter there. This is an absurd proposition. If consciousness does not have an anatomical / physical location then it is the stuff of magic and woo.
*Aside: I believe that consciousness, mind, thought, and memory are products not only of anatomy but of physiology, that is to say the ongoing electrochemical state of the brain, the constant flux of charge in and across neurons. In perfect cryonic storage, the anatomy (hardware) might be maintained, but I doubt the physiology (software), in the form of exact moment-in-time membrane electrical potentials and intra-and extra-cellular ion concentrations for every neuron, will be. Therefore I hold no faith in its utility, in addition to my indifference to the existence of a me-like being in the future.
Consider the Back-Up. Before lava rafting on your orbital, you have your brain scanned by your local AI so that a copy of your mind at that moment is saved. In your fiery death in an unforeseen accident, will the mind observed by the consciousness on the raft experience anything differently than if it were not backed up? I doubt I would feel much consolation, other than knowing my loved ones were being cared for. Not unlike a life insurance policy: not for one's own benefit. I image the experience would be one of coming to the conclusion of a cruel joke at one's own expense. Death in the shadow of a promise of immortality. In any event, the consciousness that left the brain scanner and got on the raft is destroyed when the brain is destroyed, it benefits not at all from the reboot.
Consider the Upload. You plug in for a brain scan, a digital-world copy of your consciousness is made, and then you are still just you. You know there is a digital copy of you, that feels as if it is you, feels exactly as you would feel were it you who had travelled to the digital-world, and it is having a wonderful time, but there you still are. You are still just you in your meat brain. The alternative, of course, is that your brain is destroyed in the scan in which case you are dead and something that feels as if it is you is having a wonderful time. It would be a mercy killing.
If the consciousness that is me is perfectly analyzed and a copy created, in any medium, that process is external to the consciousness that is me. The consciousness that is me, that is you reading this, will have no experience of being that copy, although that copy will have a perfect memory of having been the consciousness that is you reading this. Personally, I don't know that I care about that copy. I suppose he could be my ally in life. He could work to achieve any altruistic goals I think I have, perhaps better than I think that you could. He might want to fuck my wife, though. And might be jealous of the time she spends with me rather than him, and he'd probably feel entitled to all my stuff, as would I be vice versa. The Doppelganger and the Changeling have never been considered friendly beasts.
I have no firm idea where lines can be drawn on this. Certainly consciousness can be said to be an intermittent phenomenon which the mind pieces together into the illusion of continuity. I do not fear going to sleep at night, despite the "loss of consciousness" associated. If I were to wake up tomorrow and Omega assures me that I am a freshly made copy of the original, it wouldn't trouble me as to my sense of self, only to the set of problems associated with living in a world with a copy of myself. I wouldn't mourn a dead original me any more than I'd care about a copy of me living on after I'm dead, I don't imagine.
Would a slow cell by cell, or thought by thought / byte by byte, transfer of my mind to another medium: one at a time every new neural action potential is received by a parallel processing medium which takes over? I want to say the resulting transfer would be the same consciousness as is typing this but then what if the same slow process were done to make a copy and not a transfer? Once a consciousness is virtual, is every transfer from one medium or location to another not essentially a copy and therefore representing a death of the originating version?
It almost makes a materialist argument (self is tied to matter) seem like a spiritualist one (meat consciousness is soul is tied to human body at birth) which, of course, is weird place to be intellectually.
I am not addressing the utility or ethics or inevitability of the projection of the self-like-copy into some transhuman state of being, but I don't see any way around the conclusion that that the consciousness that is so immortalized will not be the consciousness that is writing these words, although it would feel exactly as if it were. I don't think I care about that guy. And I see no reason for him to be created. And if he were created, I, in my meat brain's death bed, would gain no solace from knowing he, a being which started out it's existence exactly like me, will live on.
EDIT: Lots of great responses, thank you all and keep them coming. I want to bring up some of my responses so far to better define what I am talking about when I talk about consciousness.
I define consciousness as a passively aware thing, totally independent of memory, thoughts, feelings, and unconscious hardwired or conditioned responses. It is the hard-to-get-at thing inside the mind which is aware of the activity of the mind without itself thinking, feeling, remembering, or responding. The demented, the delirious, the brain damaged all have (unless those brain structures performing the function of consciousness are damaged, which is not a given) the same consciousness, the same Self, the same I and You, as I define it, as they did when their brains were intact. Dream Self is the same Self as Waking Self to my thinking. I assume consciousness arises at some point in infancy. From that moment on it is Self, to my thinking.
If I lose every memory slowly and my personality changes because of this and I die senile in a hospital bed, I believe that it will be the same consciousness experiencing those events as is experiencing me writing these words. That is why many people choose suicide at some point on the path to dementia.
I recognize that not everyone reading this will agree that such a thing exists or has the primacy of existential value that I ascribe to it.
And an addendum:
Sophie Pascal's Choice (hoping it hasn't already been coined): Would any reward given to the surviving copy induce you to step onto David Bowie Tesla's Prestige Duplication Machine, knowing that your meat body and brain will be the one which falls into the drowning pool while an identical copy of you materializes 100m away, believing itself to be the same meat that walked into the machine and ready to accept the reward?