I doubt very much that bodies preserved in liquid nitrogen will be brought back to life.
I have frozen small vials of cells in liquid nitrogen. The cells must first be suspended in a kind of buffer solution (15% glycerin or dimethyl sulfoxide), which prevents water from forming crystals that destroy cells. Then they must be frozen slowly, over a couple of hours (ideally, with the temperature dropping by 1 degree Celsius per minute). Then they must be placed in the liquid nitrogen. If everything is done correctly, the cells should wake up when thawed—but sometimes don’t. I once thawed a vial of cells that behaved exactly as if they were alive—I could see them attach to the bottom of their flask, and they would change position from day to day, but they did not ever start growing. I threw them away after a couple of weeks. Other vials just never revive.
Given the host of issues that arise when trying to cryopreserve and revive cultures of cells, which are vastly less complicated than multi-cell systems such as human bodies, I have serious doubts that the technology will ever advance to the point where large, intact bodies will be thawed back to life.
I will note that tiny embryos are cryopreserved, and further note that these embryos are small enough that they do not need a circulatory system to distribute nutrients and oxygen throughout the body, and that they have no nervous system to worry about. They are *not* equivalent to adult complex organisms.
An extra complication is that the bodies are, in fact, dead at the time of freezing. Death causes massive tissue damage starting almost immediately. Skin cells can remain alive for hours after death, but brain cells, which are crucial for life as a human, die off within minutes. I don’t see how the cryo process could progress rapidly enough after death to keep the brain cells from dying.
Still, this process makes for interesting science fiction scenarios. That’s its main value, as far as I can tell.
Assuming one could freeze and thaw cells successfully, what about chemicals like neurotransmitters and hormones? Would those outlast being frozen? If not, then even if the brain and body could be thawed out, would a person’s memory be gone?
Thank you for the description of how cryogenics would need to work and which cells remain viable longer. I was in cancer detection and appreciate reading the info. Especially about the supposedly living cells in that vial.