If anything, they would be encouraged to marry a little faster. It is terribly unfortunate for both persons when they fall into fornication, because they have made the physical vows of marriage before they are fully prepared to take the verbal vows, but, the damage having been done, nothing else has changed.
It is strongly urged, however, that both members of the couple make a special devotion to learning chastity – not just so they can survive the final months of the engagement in celibacy, but so that their marriage does not fail under the weight of the selfish lust that led them to fornicate.