To a degree, you're correct. We are able to revive almost any organ, and even an entire human being, but there is a very short time frame in which this is currently possible. Extending beyond it can lead to irreparable damage to major organs, primarily the brain or central nervous system as a whole, leading to "brain death", and eventually somatic death, assuming life support isn't used to keep the remaining organ systems functioning properly. I'm quite aware, that despite how far medical science has advanced, we've still only come so far. And that's something that I feel makes this topic all the more interesting. Perhaps not from a "practical" point of view, since necromancy has historically rarely or never been practiced with the intent of long-term revival, but rather a brief encounter with the deceased either purely in spirit or in flesh by using a physical body as a very temporary conduit of communication. However, I feel that there's plenty to reflect on from a philosophical and psychological point of view. Humans have interacted with death in a multitude of interesting ways over the course of history, and still do today. This is really no different, even if it's a method surrounded by a higher amount of mysticism than other, more common means.