In Heidegger's narrative of the first movements of metaphysics, physis is associated with aletheia (and with atrekeia) and ultimately to the will-to-aletheia that paves the way for understanding things in terms of underlying (and ultimately transparent) ousiai. That last move turns aletheia into adequacy (truth as correspondence, truth as identity etc) for what matters more in physis is the very disclosure that it provides. Aristotle then states than in the fifth book of his Metaphysics that ultimately physis is ousia. The separation between the showing and concealing of what exists on the one hand and what is present, subsists and is constant is completed. The world is already replaced by a collection of entities.
Severino's neo-parmenidism has that there is no non-metaphysical nothing. That is, there are presences of absence and absences of presence but there is no ultimately nothingness beyond what is not presented. Disappearing is not annihilation unless we consider that only what is permanently exposed (ousia) counts. To depart from presence is nothing but a disappearance - and this is the pre-parricide thought that metaphysics cannot afford. Parmenides had championed an image that verges on the unintelligible for us who think in a presence-oriented key.
Object-orientation tries to leave this key aside by bringing concealment (and withdrawal) to the fore. Only objects that persist in presence, however, can afford to have real objects that are permanent. Severino's take can be approximated by the idea of a general permanentism, there is no nothingness that can be thought through in non-metaphysical terms.