All this time, ever since I first envisioned this story, all of the main characters in the book are present at this event. I finally came to accept today that this is no longer possible. With how the story has grown over the years - partly as a by-product of worldbuilding - three of the main characters cannot possibly be present at this event. Luckily, the character who actually perpetrates this event will still be there, which is good considering this event has to happen and this character has to be the one to make it happen.
But the others can't be there. And I have been wrestling with this for a while now. I've been trying to bend the plot to my will so that two of the three can still be there. But nothing worked. Any solution I concocted just felt wrong.
So, earlier today, I finally accepted that these three are just not going to be able to be there. And, once I came to that acceptance, a new door opened up and showed me how I can have these two characters learn of this event and still provide the impact it needs to upon their characters. And this has opened up a whole aspect of one character that I have been searching for. That one extra piece I've known he was missing finally solidified itself.
And the possibilities of what I can have this character do are quite exciting.
And all because I finally listened to the story and let go of a scene I've always had in my head.