I thought it would be interesting to revisit the halachic permissibility of cryonics. This previous answer mentions a view that requires >50% chance of the preserved person being brought back to life. However, what if the person who is being preserved can be viewed as being still alive?
There are two criteria for halachic death: a) No activity of heart [or possibly brain] and b) This lack of activity is irreversible.
The second point is crucial, otherwise heart surgery where the heart is temporarily stopped would be considered murder.
Similarly, if someone's heart stops we don't immediately pronounce him dead and bury him (that seems like it'd be murder too). Instead we rush him to a hospital where they can use a defibrillator and other devices to try and restart his heart. And we do everything possible, including melachos on Shabbos, to stabilize and preserve the person so he has the best possible chances to survive being transported to the hospital. Even if the chances of restarting his heart there are low.
This is all because as long as the lack of activity is reversible he is still considered alive.
Can cryopreservation be viewed as simply another technique that stabilizes and preserves someone so that he has the best possible chances of being resuscitated? The difference here is that instead of preserving him to survive the transport to a hospital, we preserve him to survive the passage of time until the technology to resuscitate him becomes available. From this point of view, we are not cryopreserving a dead person. Instead we are preserving someone who is still alive and able to be revived, from irreparably destabilizing and decomposing (i.e. dying).