Non duality is the state of oneness of existence and there is no scope in its philosophy for anything like non-existence.

Formless soul or Consciousness is the witness that experiences the action, the actor, and the world of separate things. It is like a light that illuminates everything in a theatre, revealing the master of ceremonies, the guests, and the dancers with complete impartiality. Even when they all depart, the light shines to reveal their absence.

What is not consciousness (formless) in the experience of diversity (universe or waking)?  The waking and the dream cease to exist without consciousness.  The seeker, seeking and his destination   all are one in essence.

For Gnani, who is aware of the fact that the self is not physical but self is consciousness, there is no illusion, even though; he is in the midst of illusion, because he is fully aware of the fact that, all the three states are consciousness.  Therefore he is conscious of consciousness in the midst of the illusion. 

The language of the duality, invented by the within the duality, for use in the dualistic world, when used to describe non-duality, produces these apparent contradictions, because there no apparatus in non-duality, because noting exist other than the soul, which is in the form of consciousness.

Non duality is the state of oneness of existence and there is no scope in its philosophy for anything like non-existence.

Gaudapada’s rational exposition of Advaita:- that whatever is seen, whether external or internal, whether by the ordinary persons or yogis, is unreal.

The essence of Mandukya's is: Do not be satisfied with rituals, yoga etc. which are good in their own way, but inquire. Inquire into the nature of the mind. ? Brahman and Atman are things one can never see. So seeker should not inquire into them.  He has to inquire into the world around him, which he can see. The analysis   tells him it is passing away every second. Everything is dying repeatedly. Where is it going? Thus he follows up his investigation into what he can lay hands on. How can he inquire into Atman which he cannot see? So first he must deal with the known and seen, this inquiry leads up to the unknown in the end.

Mediocre minds waste their time on arguing about unimportant matters. Accumulation of scriptural knowledge is dangerous in pursuit of truth. The seeker has to establish in the truth of Non-duality by sheer reasoning alone. The seeker has to begin by defining "What is real?" "What is unreal?" etc, because that is the right way to discuss, understand and assimilate Self-knowledge or Bramha Gnana or Atma Gnana. 

By becoming more and more intellectual one becomes more and more intoxicated to individuality. The intellectuality is limited to duality.  In the realm of truth the intellectuality is replaced by non-dual wisdom.  There is nothing exist other than formless non dual existence. Therefore, there is   no individual to become sane or insane. There is no second thing exists, other than consciousness.  Everything is one, that is, unity in diversity. The curiosity, urge cannot be imposed on others.  It has to sprout within. One need not become a guru because the guru is within guides every seeker.

 If one is aiming to be a master, Guru or teacher, he will never reach his destination. One has to share his knowledge with the fellow seeker not to make them his followers but only direct them if they are interested to travel beyond form, time and space.

It is foolish to impose our idea on others because everyone is not in the same level of understanding.  Every one's inner work is on. When they are ripe enough they will understand, assimilate and realize on their own.  If they are ready and sharp enough they will grasp it instantly and they will reach their destination with lesser time and effort. Thus preaching, teaching is not wisdom, but by very careful reasoning, the seeker has to determine the nature of reality. Thinking in right direction alone helps seeker determining the nature of reality.