J tells us in the Course that our reality is a complete lack of separation from one another, where there is no "gap" between us at all. He tells us that, consequently, "we are one", the "one Son" of God. Does this mean that there is literally only "one" kid? Not a chance.
Oneness need not be confused with a literal singularity, where all of God's children somehow collapse and implode, morphing together into some kind of "God blob" where all Identity is lost. J is teaching us to lose our fear, not our Souls. Oneness simply refers to the One Mind in which we live eternally - right NOW and forevermore!
The problem we seem to have is that, in spite of that One Mind in which we live NOW, we have a crazed belief in the illusion of separate bodies. God's children (plural) believe we live within the confines and limitations of bodies and must communicate through ears, mouths, touch, etc., but not by way of the only real means of communication, which is the Mind we all share. For, the body and all of its tools are in and of the Mind, as well, ironically enough for us.
By way of J's tools for healing which he brings to us, such as the miracle and forgiveness, we begin to recognize and remember our true Identity as spirit and mind, rather than the illusion of body. The experience of revelation, while indescribable, does demonstrate by direct experience that union with the perfect Love of God and our brothers beyond the limitations of form is what Heaven really is! J tells us in the original manuscripts of the Course that oneness simply means to be of one will. He also tells us that the Kingdom of Heaven is YOU! Please take great delight in knowing that oneness is the condition of ALL of the Sonship's members residing together in union with God, our Father.
While the body absolutely disappears as it is forgiven completely and no longer valued, the creations, the "Christ Kids" of God's, CERTAINLY never disappear! Only the ego's fatalistic thought system would attempt to ascribe God's Heaven and the state of Oneness as a "place" where God's children disappear. How fearful is that thought, and how much clever resistance to J's Guidance the ego has established by considering oneness in this way.
Ask yourself this question, just as Victor Wooten expresses it on behalf of God in his song, "I Saw God":
"If I only have one Son, then tell me, who are you?"