That given sufficient quantum instability, in an extremely primordial or degenerate universe wave-functions may collapse in such a way as to tunnel or jump past the event region, thereby transiting into a state of antiprobability.
(Note that in this state they would not have a negative probability, as certain quasiprobability distributions are said to have, nor any other anomalous probability value such as a variable. They would thus exist in a very exotic state indeed, since they could neither be concrete [probability =1] nor impossible [probability =0], nor could they exhibit any level of probability in between.)