Then, one day, the are told their important and distant "parents" are finally arriving to bring them away to their new life...
Anyway, the point is that any aging wealthy pedicidal murderers are also gonna insist the body is perfect before they move in, meaning some other brain is going to be doing the work.
And you also reminded me of the flawed but moving film "Never Let Me Go" from 2010 about a more present version of this. Oh, and there's also Michael Bay's "The Island".
(In practice, almost everything over 5 years away, even when already in early human trials, has this property; the only reason the Covid vaccines happened faster is that everyone was willing to throw unlimited resources at the problem and do simultaneous tests on all candidates, and in a pipeline, rather than cost-efficiently and slowly like everything else has been).
In-vitro tissue culture is already a thing (including brain organoids, if you want a brain to control a robot: https://en.wikipedia.org/wiki/Cerebral_organoid), as is 3D bio-printing.
IIRC, there's no current way to scan even a single living synapse/synaptic cleft/dendrite combination to read out the corresponding connection strengths, let alone for the whole brain, so we can't yet scan a brain — but if we could do that, writing it back to a fresh blank one currently seems(!) like the easy part, as neurons change shape and grow in response to electrical gradients.
This, er, Brain of Theseus would retain operational patterns even if the individual cells have been replaced.
A variation on that would be too do it stochastically, constantly substituting a miniscule percentage of cells evenly across the entire brain.
This thread is about stem cells in monkeys.
https://blanu.net/curious_yellow.html
https://en.wikipedia.org/wiki/Glasshouse_(novel)
h/t HN user cstross