Hello, I missed the one Siyum in the town. Was I required to fast?

ב"ה Shalom and Mo'adim Lesimcha. In principle, you should have fasted, since this is a Din written in Shulchan Aruch, however there are other circumstances for which we can say that after the fact maybe you didn't have to fast. The Mishna Brura ( שו"ע סי' ת"ע ס"ק ב) says that if one fears that if he were to fast erev Pessach he will not be able to fulfill the Mitzvot of the seder night due to fatigue and weakness, he should not fast. Better yet, wrote the Mishna Brura would be to eat only light food. All the best Chag same'ach and Shabbat Shalom