So very many people will die before the advent of working rejuvenation medicine, largely from aging, and including many of you reading this now. The only viable option open to these folk is cryopreservation, the low-temperature storage of the brain and body after clinical death. This process can preserve the fine structure of the brain sufficiently well for plausible future technologies to revive a preservee; everything that makes you the person you are is in the structure of your brain. Preserve that, and you can wait as long as needed for the expanding future of medical nanotechnology - and even more advanced science beyond that - to develop the needed tools for revival.
Very low temperatures create conditions that can preserve tissue for centuries, possibly including the neurological basis of the human mind. Through a process called vitrification, brain tissue can be cooled to cryogenic temperatures without ice formation. Damage associated with this process is theoretically reversible in the same sense that rejuvenation is theoretically possible by specific foreseeable technology.
Injury to the brain due to stopped blood flow is now known to result from a complex series of processes that take much longer to run to completion than the 6 min limit of ordinary resuscitation technology. Reperfusion beyond the 6 min limit primarily damages blood vessels rather than brain tissue. Apoptosis of neurons takes many hours. This creates a window of opportunity between legal death and irretrievable loss of life for human and animal subjects for cryopreservation with possibility of future resuscitation. Under ideal conditions, the time interval between onset of clinical death and beginning of cryonics procedures can be reduced to less than 1 min, but much longer delays could also be compatible with ultimate survival.
Although the evidence that cryonics may work is indirect, the application of indirect evidence is essential in many areas of science. If complex changes due to aging are reversible at some future date, then similarly complex changes due to stopped blood flow and cryopreservation may also be reversible, with life-saving results for anyone with medical needs that exceed current capabilities.
If you're interested in living to see the bright future of humanity, but unlikely to survive into the near-future era of rejuvenation medicine and enhanced longevity, then cryonics is the only practical way forward. Nothing in the laws of physics prohibits medical technologies capable of restoring a cryopreserved person to life and function - if the structure of the preserved brain is intact, it's just a matter of waiting.