It appears inevitable that we can fully map a dead person's neurons and synapses. [1] is doing essentially that for a tiny sliver, with some amazing images to show. From there, it's "just" scaling up.
That alone wouldn't be enough to fully clone a person's consciousness. There is information stored in the actively firing synapses. For example short-term memory seems to be stored by sending signals in a loop, and there might be more such mechanisms. Those signals are obviously lost once the brain is dead. Another issue are hormones. The same brain regulated by a different (simulated) body might behave completely different. And then there are probably a lot of unknown unknowns. Despite decades of research there are still a lot of open questions, and more questions will become apparent once we actually start simulating complex brains.
But that doesn't mean that those early methods wouldn't be useful, both for science and for more questionable efforts. For example accessing the long-term memory of a recently deceased might be comparatively viable if given enough funding
1: https://edition.cnn.com/2024/05/15/world/human-brain-map-har...
> From there, it's "just" scaling up.
I suspect this wasn't your intention, but I feel this heavily undersells how much work is involved in "scaling up" to simulating a human brain. I wouldn't even say that it is inevitable, because there are so many unsolved questions and unknown-unknowns.
There are decades of research and we are still an unknown and large number of years away from doing this. Fusion power is more tractable that this.
It's not even clear whether our current approach to computation will ever be able to do this. We might need completely novel types of computers, maybe organic-machine hybrids.
I'm not even touching on the very real and serious ethical questions of simulating human level consciousnesses.
Hence the scare quotes around just.
Also note how my "just" only applies to scaling from mapping a grain-of-rice-sized piece of human brain to mapping a full human brain. Going from there to simulating it would be another big leap, never mind the challenges to simulate it in a way that actually produces results comparable to the actual brain of that person.