The Immortality Paradox

It is the greatest wish of those destined to die to subvert their inevitable fate, but the achievement of true immortality is an elusive endeavor that has vexed even the greatest minds.
It is the lot of post-Diminishing beings that their time in the world is decidedly finite. Even the descendants of the Primordial Titans cannot survive the relentless march of time, even if they do exist on a scale of time orders of magnitude greater than the likes of Humans. The reason for this is that over time, the spiritual bonds that entwine body and soul breakdown. This gradual wearing happens irrespective of the physical state of the body (though the degradation of the body can speed the process). For the average mortal, this breakdown happens at a far slower pace than the physical aging process and is thus a non-issue for the vast majority of people. For those wishing to survive past their cosmically-decreed lifespan, this spiritual entropy becomes a far more pronounced problem the longer they are able to stave off the decay of their bodies.
Ironically, despite the massive disparity in normal lifespans between the various mortal races, it seems to be a universal constant across souls that a thousand years is the upper limit for how long they can remain grafted to its owner's corpus.
Preventing this inevitable separation has been the subject of the study of many a wizard and warlock seeking life beyond their means. Despite this, there are only a small handful of methods that have been proven to fortify the souls bonds or otherwise prevent it from being pulled into the Outer Planes. Unfortunately, all of them are exceedingly difficult to conduct, ethically and morally depraved, a matter of circumstances outside the practitioner's control, or some combination of the three.

1. Lichdom.
The practice of manually cleaving soul from body and sealing it within a phylactery is a surefire way to prevent the soul from passing into the Great Beyond. Unfortunately, the rituals required are deeply esoteric, very easily botched (resulting in catastrophic results for the practitioner), and usually require hefty human sacrifice.
2. Stasis Fields.
In remote parts of the world, there are Foci that have become so intertwined with the land around them that they create demiplanes within the Material Plane that are saturated in their primeval magic. In precious few instances, this phenomena results in a space that preserves the lifeforce of those residing within it. While this does result in effective immortality, it is restrictive in that it leaving this field, especially after lengthy furloughs within, can result in rapid deterioration of the body/soul connection.
3. Pure Luck.
Every so often, an individual simply seems to be bestowed with a Boon of Immortality. For whatever reason, these individuals simply do not experience the normal degradation of the soul that others do. This could be because of the blessing of a god, a certain state of enlightenment, exposure to acute, transformative magic, or, again, just pure, dumb luck. Many wizards have tried to artificially recreate this phenomena, but to date, none have succeeded.