Let's assume that at least "one" existence of "something" is possible, and that it corresponds with the one that you, the reader, are assuming to be experiencing right now. Somethingness.
Okay, then let's make the leap and say it's possible that nothing could be.
At this point, the odds of nothing existing are 1/2, because the set of possible universes is [nothing, something]. And if we go by the assumptions that every possible state in this set of possible states is equally likely (a common assumption in classical probability theory), but that only one state can be actualized, then this is leaving us with 1/2.
But then think about all the possible "existences" that could exist as different combinations of the substance around you. The state space is huge. Nothingness forms a vanishingly small part of that set of possible existences. The thing is that one form of "nothingness" is indistinguishable from another form of "nothingness". By extensionality, the set of possible existences only contains "nothingness" one time.
This is a naive set theory/classical probability theory approach to the question.
Of course, in a multiverse idea of reality, we don't necessarily have to pick one of the possible existences. They can be in some kind of larger superposition, even if they are somehow cut off from one another. Maybe nothingness is compatible with somethingness. We existers just don't happen to experience it. And how could we? What is there to experience and who is there to experience it?
Wow. Enough is enough! I feel like a wide-eyed college freshmen again!
Bye :)
P.S. It occurred to me that there might be distinguishable variations on non-existence. For example, what if the set of possible realities is: ["Nil", "nada", "null", "nothingness", "pitch black silence", "non-sense", "eternal vacuum", "something"]. Well then in this case, we are sure lucky to be here! There was a 7/8 chance that some form of nothing would be the ultimate reality!