A billion people will die between now and the earliest plausible date for the first package of rough and ready but working rejuvenation therapies - say twenty years from now. Another few decades will pass for the technology to work its way out to global availability at low cost, and the deaths by aging will continue in less fortunate regions while this happens. Even after aging is completely conquered, there will be an ongoing toll of death due to accidents and whatever passes for disease in the age of medical nanotechnology. Death isn't going away completely for we biological folk, no matter how well we do in the field of medicine in the foreseeable future: medicine can't wave away falling rocks.
Thus will always be a role for what we might term post-mortem critical care: technologies and services to preserve the fine structure of the brain and the mind it contains following death, and keep them preserved until such time as that patient can be restored to life. At present the only post-mortem critical care option is cryonics, with what looks like a fair few years to wait for technology to advance to the point of restoration, and thus an unknown chance of eventual success for any individual - but a significantly greater chance than is offered by the grave, of course. In contrast, in a future in which the technology to restore a preserved person exists, cryonics and other preservation technologies like plastination will occupy a more dynamic position in the medical toolkit, and patients might expect to wait in a preserved state only for transport to the nearest major population center.
Cryonics involves the cryopreservation of humans as soon as possible after legal and clinical "death". Legal and clinical death differ importantly from biological death or true (irreversible) cessation of function. It is therefore a mistake to portray cryonics as an alternative to cremation or burial. It is true that cryopreserved people are not alive but neither are they dead. Cryonics should be seen as part of the field of life extension. Cryonics enables the transport of critically ill people through time in an unchanging state to a time when more advanced medical and repair technologies are available. Even after "longevity escape velocity" has been attained and aging has been largely tamed, cryonics will continue to be needed for people who die of accidents or diseases for which there is no cure at the time.