Please realize I write this from my own particular viewpoint. I am not saying I'm right... but this is what my experience has led to.
However, when the partial consciousness connects with the "one" consciousness, does the individual loses its individuality?
In our usual conventional sense of individuality, yes. Individuality is a temporary function. Our ego is ephemeral and eventually ceases to exist- it is a temporary dream or art work of the Divine. Only the Divine is lasting. The part of us that is eternal is found in being an extension of Her Being.
In moments I have experienced merging with the Divine, I was nothing but sound and vibration within Her sound and vibration. There was nothing else. At this point, I can mostly choose how much to step into that realm of experience and being, as opposed to stepping into my sense of egoic self, the flows of time, and the trajectory of this sound that I am within the greater river of the Divine. The purpose in doing this is two-fold: to live as art and to find the pleasure of incarnation, which the Divine experiences through all of us as extensions and also, to lift incarnate extension to the light through me, so that there is a harmonious flowing between the Divine and all Her myriad material art works.
There really is no "I." I am ultimately an extension of Her light. My highest purpose is to express this within time and space, within the realm of form and forgetfulness... until I once again fully merge with Her and find what is actually myself.
So eventually, there will be left only this "one" consciousness and no individuals.
Well, yes... provided the Divine does not continually create new art. Perhaps this will never come to pass, perhaps it will. It is impossible to say. But if the Divine stopped unfolding into the art of existence, then yes, all would return to Her and individuality would cease... we would return to the state of singularity before She began to compose the symphony that is all the multiverse.
If so, all the sages that manages to merge with the one consciousness will no longer exist as individual sages and we should not have the existence of individual sages in our midst. This does not seem to accord with the reality that there are many individual sages in the past and at present.
If an individual reaches full merging with the Divine, they are no longer an individual sage, but a vessel or extension of the Divine Itself.
We may perceive them as individuals, but that is our own faulty understanding. Our own misunderstandings do not define what is truth. They only demonstrate our limitations in perception.
While we are in an incarnate form, we may take on an individual personality. It is possible to become fully merged with the Divine and still be alive in an incarnate form. In this case, one plays with individuality, knowing deeply that it is not reality, but merely a temporary form of art. One's self becomes a canvas on which to paint a reflection of the Divine... but one realizes that ultimately, the canvas will disintegrate and only the connection to the Light and Love remain. It is the energy of relationship that lasts- of finding the true self, which is held in the Limitlessness of the Divine Embrace.
"A" being can realize increasingly wide levels of mutual group consciousness and play in each of these, constricting down to a single "individual" and expanding into ever-farther-flung networks of the extension of the Divine... all while realizing, moment to moment, that all of this is temporary. It is performance art, but art with a purpose of remembering, of awakening to the reality that is the One Divine Being Itself.
Dropping the illusion of disconnect, of individual self-hood... this allows true freedom in individual action, thought, and feeling. What happens is that the divine self within awakens to its true potential and place as an extension of the Divine, having never left Her embrace, but only forgotten that he is in It. At that point, one is awakened to the creative potential of using one's own self- the consciousness, the emotions, the sensory world, actions, intentions, will- as a medium through which to express the temporary experience of an everlasting force.