There are two competing theories.
In one theory Oblivion is the calcified and congealed hate of the Neverborn, their manifest desire to cease given location, if not necessarily form. In this theory Oblivion is merely the result of their nature as dead-but-dreaming corpses. The only reason they continue to exists is because their hate for everything else eclipses their desire to cease. In other words, much like the Elemental Pole of Fire is the ultimate manifestation of the Primordial deciding that Fire was going to be a thing, Oblivion is the desire of the Neverborn to Be Not. In this case, it is no more metaphysically potent than anything else a Primordial or group of Primordials could create. This is pretty damn potent, mind you, but it means it fails against any effect which would be perfectly indestructible. So you could, for instance, activate a perfect environmental defense effect and just walk around in Oblivion with no more care than you would walk around in the Pole of Fire or Adorjan’s Wind.
This is, more or less, the canon interpretation of Oblivion. The later 2e authors had a hate on for Abyssals and anything to do with them, so everything to do with them was hit with the nerfbat pretty heavily. This means that Oblivion could never destroy everything, because some things are indestructible. Abyssals, for example, don’t draw on Oblivion directly but are instead drawing on the Neverborn and get Oblivion-themed stuff because the Neverborn created Oblivion, much in the same way Infernals get green fire stuff because Malfeas created Ligier.
The other theory is that Oblivion is something that predates or was discovered by the Neverborn when they died. A sort of universal constant, a null state to which everything eventually returns. In this theory the Neverborn are no more connected to Oblivion than anything else, they’re just too attached to Creation to slip away. Perhaps Oblivion is the anti to Creation’s matter, or the natural result of using Nigurna as the fundament of existence or some even older and deeper law than even the Primordials understand.
In this theory, if you get drop kicked into Oblivion you are Dead. Perfect defenses would only apply in the “avoid being dropkicked into it” phase of the event. If you willingly jumped in, you cease to be. Your Exaltation probably rips out of your body moments before it is also annihilated as well, otherwise it would be gone.
I prefer the latter theory.