A little theory regarding the Dokis and Act 2 along with Sayori herself.
We've seen how....unique DDLC is during the gameplay regarding acts 1-4 but Act 2 made a huge impact in terms of how Monika, Yuri and Natsuki are the only ones left.
With Sayori gone, everything goes downhill from the beginning....but it's not just because of her death at the end of Act 1.
It's because of how she's the key to holding the club together.
We've seen in DDLC Plus, she was the first person to join the club before Natsuki and Yuri along with becoming vice president.
She stopped Yuri and Natsuki from fighting, comforted Yuri, befriended Natsuki and trusted Monika with her depression.
She has the traits of being A'habbat's daughter along with Rosie.
But this is where the theory starts....
What if Sayori's death had a trigger effect not only on the game....but also their world?
Not only for Act 2 but if you delete Monika early in the game.
Here's what happens when you delete Monika very early.
After it closes the game, it'll show a picture of Sayori's death and a message that appears after ten minutes saying "Now everyone can be happy".
It shows a connection with the Scarlet King formerly believing that existence is pain and since Sayori becomes aware she's in a game, she'll find it very painful to exist since she now knows she's not real.
Since she's A'habbat's daughter, she has the traits of her being the seventh bride due to her kindness and energy....but if she becomes self aware like Monika....realizing she's part of a game and nothing more....she'll find existence is pain and could possibly go down the Scarlet King's path.
That's why if she dies, the game can't function without her or her traits as being the daughter of the seventh bride.