Existence is not rendered obsolete through the spiritual work. Such an assumption implies that God has no purpose, which is a very strange and alien concept within esoterism. That is rather a belief commonly held by atheists, not initiates.
The purpose of the spiritual work is to become more active as a consciousness, more useful for humanity, as symbolized by the Cosmic Christ: Avalokiteshvara. Christ consciousness is pure activity as a level of being. Even though there is peace and equanimity in the state of a God, the Lord manifests and expresses across countless planets, solar systems, galaxies and infinites. Just because a human being reaches perfection does not mean there is no more to do: in fact, we can state that the path has only truly begun. According to one Sufi master, "The path to God is short. The path in God is infinite."
It is also the law and obligation of Christ to help new souls achieve Christification upon reaching our own. The law of Christ is sacrifice. Just as we have been helped with this knowledge, so too must we help others if we indeed achieve self-realization.