The Torah avoids spelling out specifics about events that will occur in the future because were the Torah to say what will occur, then those events will inevitably happen and there would no longer be an opportunity for bechira. (R' Tzadok HaKohen explains that Avraham is credited for his affirmation of belief in the promise of children and yerushas ha'aretz he received in Parshas Lech Lecha, "Vayachshevaha lo tzedaka," because it required his trusting that nothing his children or grandchildren would do would interfere with that promise being fulfilled -- Klal Yisrael's destiny transcends bechira.)
This is why perhaps the most remarkable pasuk in the megillah is, " Mordechai lo yichra v'lo yishtachaveh." The pasuk is written in future tense -- Mordechai will not bow down. It's a promise of what will happen, not just a report of what did happen. No matter that every individual has free choice to decide whether or not to bow to Haman. There will always be someone, that Mordechai hatzadik, who will remain standing and not give in.
Sefas Emes explains that the future tense is used because the megillah is speaking to all future generations. In every time and place there will always be a Mordechai who will not bow his head. The megillah does not at first tell us Mordechai's name. Our hero is introduced with the generic appellation "ish yehudi," a Jewish man, a somebody -- "Ish yehudi haya b'Shushan habirah...." That "ish yehudi" could be anyone. In those days he happened to be named Mordechai, but in another time and another place he could have some other identity, some other name -- but he will always be with us.
This is why Haman wanted to destroy the entire Jewish nation. Haman realized that Mordechai is the yotzei min ha'klal that is melamed al ha'klal, the exception that proves the rule. Were he just to defeat this Mordechai, there would be just be another Mordechai, another ish yehudi, who would step up and take his place.