If the breakthrough was unsuccessful, that would mean reaching the realm of a Great Divine Transcendent, with the body beginning its partial transition into primality.
Indeed, the so-called Great Divine Transcendents are cultivators at the peak of Quasi-Saint perfection who failed to break through to become Daluo Jinxian of the Primordial.
Although they failed, their bodies have begun to transform and possess some characteristics of the Daluo Jinxian of the Primordial, hence their strength is far superior to Quasi-Saints but still not on par with Daluo Jinxian of the Primordial.
Failure in the breakthrough is quite normal, with Donghuang Taiyi being the only one since the Taoist Ancestors to directly integrate the Slaying Three Corpses and successfully leap from the peak of Quasi-Saint into the Realm of Primordial Chaos. The rest, without exception, all became Great Divine Transcendents.