Very complex question, muddied by consideration of whether the 1917 Code still holds or the 1983 Code is valid (i.e. whether you're a sedevacantist).
Did you know before you had intercourse that the woman would in fact take a morning after pill? If not, then you did not incur excommunication.
If you knew, I believe that the 1983 Code (and JPII's interpretation of it) is actually more strict than the 1917 code, allowing accomplices to more readily incur excommunication.
Also, the problem with such, especially in the 1917 Code, is that the penalty was incurred only IF the abortifacient produced an actual abortion, which you would likely not know. Some canonists held that the penalty was not incurred unless it was CERTAIN that the effect (abortion) had been produced.
In one sense it's a technicality, but there's no question that grave sin was involved, not only because of the fornication (or adultery) but also due to a reckless disregard for a possible outcome which might entail an abortion. It's like driving around drunk. While you may not have actually killed someone (because you were lucky), you were still putting lives at risk and causing the potential to kill someone, like flailing a loaded gun around recklessly and having it discharge into someone (or miss them) vs. taking direct aim and pulling the trigger.