Any non infinitessimal probability leads to certainty given enough time.

Consider it in terms of reactions per second - take the likelyhood of non-formation of replicators (call it 99.999999999% - because it actually does not matter), to the power of the number of reactors, to the power of the number of seconds since the universe began.

The likelyhood that no self-replicators form rapidly plummets to a vanishing value.