What is so important about the Bigsan and Seresh subplot?

Question

In the Megillah, Mordechai saves the king's life from Bigsan and Seresh, and by doing so, he ultimately gets paraded around the city by Haman.

Let's say that this subplot never happened. How would the story have been different? Esther still would have been queen. Haman still would have wanted to kill the Jews. Mordechai and Esther still would have had their fasts and their conversation. Esther still would have asked Achashveirosh and Haman to her parties, at the latter of which she still would have had Haman killed.

I see two differences between these two plotlines. First, if Mordechai wasn't in the king's book, then the parade wouldn't have happened, obviously. But more importantly, if Achashveirosh could sleep that night, not having an unsettled account rattling around in the back of his mind, Haman would not have been able to ask about the gallows in any event; and if Achashveirosh couldn't sleep, perhaps the officers would have been able to get him to sleep with the Royal Chronicles, which was their goal even as the story actually played out. So ultimately, while that night would have played out differently, the end result presumably would have been the same.

The second one is Charvonah's jumping in at the end of the second banquet. If Haman was trying to kill Mordechai, who had saved the king, what else would Haman do? So Achashveirosh killed Haman. But let's say that Mordechai never saved the king. Charvonah still might have accomplished something: after all, Mordechai was still an advisor to the King, as we see from 2:19:

וּמָרְדֳּכַ֖י יֹשֵׁ֥ב בְּשַֽׁעַר־הַמֶּֽלֶךְ

And Mordechai was sitting in the palace gates

as explained by Megillah 13a:

אזיל שקל עצה ממרדכי אמר אין אשה מתקנאה אלא בירך חבירתה ואפי' הכי לא גליא ליה

[Achashveirosh] went to get advice from Mordechai [on how to get Esther to tell her nationality]. [Mordechai] said: "Nothing makes a woman jealous like the thigh of her friend." But even so, she did not reveal to him.

Since Achashveirosh obviously held Mordechai in high regard anyway, Charvonah still may have had his intended effect.

So what part of the story would have been different had the Bigsan and Seresh subplot not happened? (That is to say, they never plotted to kill the king.)

Answer 1

If Mordechai never discovered the Bigsan and Seresh plot, then he would have (presumably) been executed by Haman.

When Haman came to ask the king permission to hang Mordechai, the king interrupted him (before Haman could reveal he wanted Mordechai dead) and proceeded to reward Mordechai. Haman from that moment on (it wasn't the parade that mattered) would never have the guts to mention killing Mordechai again. Even if the king was asleep, Haman would have come in the morning to secure Mordechai's death warrant instead. He would have been granted it, since Mordechai was violating the king's order to bow down to Haman.

So, with Mordechai's death, the Jews would not have a powerful representative at court. So, when the new decree would be issued allowing the Jews to stand up and defend themselves, the enemies would not have been so intimidated by it. But, with Mordechai as leader, they were intimidated. The Megillah mentions proof to this by reciting how much the people were in awe and respectful of Mordechai and his power etc.

Answer 2

To add to the excellent answer by David Kenner, note that Charvonah, when reporting the gallows, notes that it was built to hang Mordechai who spoke good to the king (I.e. saved his life!) I remember seeing somewhere that this was an important part in ensuring Homon's immediate execution, as it made it appear he was planning a coup. The need for his immediate execution being important both to prevent any chance of him avoiding it if he went on trial etc, and also to immediately undermine the standing of his pet project to massacre the Jews.

Answer 3

According to the Malbim, the whole reason why Achashveirosh promoted Haman to second-in-command was because Haman took credit for saving Achashveirosh’s life. If the Bigsan and Seresh story never happened, the whole Megillah, from the 3rd Perek on,would never have occurred. Malbim Esther 3:1

Answer 4

Chacham Tzvi says:

The king did not trust Haman, thinking he is bent on killing him.

Once Haman's enemy Mordechai reports the plot and no report of Haman being involved, only then did Haman regain trust and then was elevated to the highest position.