"Ontological nihilism" is defined as the position that nothing ultimately exists. Now, I'm writing this post not to debunk something so obviously false as ontological nihilism. Rather, it's my purpose to argue that in any possible world w1 at which something exists, it is impossible for there to ever be a state of affairs in w1 at which nothing exists.
1. Something x1 exists in w1. (Premise)
2. There is a time at which x1 fails to exist in w1. (Assumption)
3. Either some other entity x2 exists in w1 or else nothing continues to exist in w1. (Implied by 1 and 2)
4. If nothing continues to exist in w1, then there is a final moment of time in w1. (Premise)
5. At any final moment of time, whatever exists at that last moment will continue to exist in a changeless state. (Premise)
6. Hence, if time fails to exist in w1, then something will forever exist changelessly in w1. (From 4 and 5)
7. Therefore, the existence of x1 implies that "nothing exists" in w1 is necessarily false. (From 4 and 6)
In short, time is a measurement of change. If all things fail to exist in w1, then that constitutes a change in w1. However, if there is a final moment of time, then that final moment will forever be a changeless present. If this changeless present does not exist, then it is meaningless to speak of any past time. Since tensed facts are meaningful, it follows that a changeless present would have to exist. Therefore, for any possible world at which something exists, it is impossible for nothing to exist in that world.