If we take into account all the countless lives/experiences we have had of non-awareness intervoven with awareness it shows that we already have a vast experience of both ”existence” and ”non-existence”.
Just take the first few months as a newborn with
no ”proper” awareness or even any clear memories.
Now multiply those few months over the span of countless hundred of thousands of lives as a newborn + all countless moments of dreamless sleep and all the moments of being unconscious, for whatever reason.
Also not being able to remember something
despite ”being there”.
Bottom line, the reality of ”non-existence - no awareness” & ”existence - awareness” is already hardwired into our very experience and nothing unique and requires no effort at all to achieve. We go between these two states of being and not-being all the time.
Even universes expand and contract…
So in that very sense non-existence, just like existence, is also anicca, dukkha, anatta since: ”separation from what is pleasing is suffering”, ”not to get what one wants is suffering”
Vibhava-taṇhā (craving for non-existence)
Bhava-taṇhā (craving for existence)
The path leads beyond existence & non-existence, beyond being and not-being which despite whatever preference one happens to have never becomes a permanent reality in Samsara; which is a endless wandering between existence and non-existence.
What non-existence is and implies is already something firmly established and have been experienced by pretty much all beings already, just like existence.