Not necessarily less you. Why even replace? What about augment?
Add an extra "blank" artificial brain. Keep refining the design until the biological brain reports feeling an expanded memory capacity, or enhanced clarity of newly formed memories, or enhanced cognition. Let the old brain assimilate this new space in whatever as-yet poorly understood pattern and whatever rate comes naturally to it.
With the patient's consent, reversibly switch off various functional units in the biological region of the brain and see if the function is reconstituted elsewhere in the synthetic region. If it is, this is evidence that the technique is working. If not, the technique may need to be refined. At some point the majority of the patient's brain activity is happening in the synthetic regions. Temporarily induce unconsciousness in the biological part; during and after the biological part's unconsciousness, interview the patient about what subjective changes they felt, if any.
An agreement of external measurements and the patient's subjective assessment that continuity was preserved would be strong evidence to me that such a technique is a reliable means to migrate a consciousness from one substrate to another.
Migration should only be speeded up as a standard practice to the extent that it is justified by ample data from many different volunteers (or patients whose condition requires it) undergoing incrementally faster migrations measured as above.
As far as cryonics goes, the above necessarily requires actual revival before migration. The above approach rules out plastination and similar destructive techniques.
I agree with all this, except maybe the last bit. Once the process of migration is well understood and if it is possible to calculate the structure of the synthetic part from the structure of the biological part, this knowledge can be used to skip the training steps and build a synthetic brain from a frozen/plastinated one, provided the latter still contains enough structure.
Anyway, my original question was to scientism, who rejected anything like that because
Any account that involves a step where somebody has to create a description of the structure of your brain and then create a new brain (or simulation or device) from that, is death. The specifics of your biology do not enter into it.
In June 2012, Robin Hanson wrote a post promoting plastination as a superior to cryopreservation as an approach to preserving people for later uploading. His post included a paragraph which said:
This left me with the impression that the chances of the average cryopreserved person today of being later revived aren't great, even when you conditionalize on no existential catastrophe. More recently, I did a systematic read-through of the sequences for the first time (about a month 1/2 ago), and Eliezer's post You Only Live Twice convinced me to finally sign up for cryonics for three reasons:
I don't find that terribly encouraging. So now I'm back to being pessimistic about current cryopreservation techniques (though I'm still signing up for cryonics because the cost is low enough even given my current estimate of my chances). But I'd very much be curious to know if anyone knows what, say, Nick Bostrom or Anders Sandberg think about the issue. Anyone?
Edit: I'm aware of estimates given by LessWrong folks in the census of the chances of revival, but I don't know how much of that is people taking things like existential risk into account. There are lots of different ways you could arrive at a ~10% chance of revival overall:
is one way. But:
is a very similar conclusion from very different premises. Gwern has more on this sort of reasoning in Plastination versus cryonics, but I don't know who most of the people he links to are so I'm not sure whether to trust them. He does link to a breakdown of probabilities by Robin, but I don't fully understand the way Robin is breaking the issue down.