Iacob, the "Last Good Man In The Galaxy" is at the head of a massive fleet of refugees when it is attacked by pirates. Upon capturing the queen of the fleet, he simply asks her why she did this. She tells him they have no choice. Iacob tells her that's not good enough and points out that the refugee fleet is made up of dozens of different races and, because the fleet is so large, they could have become an armada bigger than ever seen before. Just to prove his point Iacob lets the queen free and she escapes. Later, the same fleet reappears fully armed and seemingly ready to attack the refugee ships. The desperate admiral of the fleet readies himself for the end.... Only for the pirates to fall into formation with the refugees.
Ch 32: the remaining loyalists primarchs are united again.
Ch 40: Nemesor Zahndrek and Vargard Obyron's last exchange before their deaths. For context, Zahndrek is a Necron who is under the delusion that he is still fighting against the C'tan— essentially making him an old, senile, Shell-Shocked Veteran.
Zahndrek: "Is this victory? Have we won at last?
Obyron: "Yes, my Nemesor. Yes."
The Silent King had ended the War in Heaven, once and for all, by committing what amounts to a complete genocide of his own race- and uploading the souls of the remaining, unchained Necrons into Pariah humans, fusing them together, thus creating Human-Necrotyr Hybrids.
"The Necrons are dead, for the most part,” she (a female Necron, upon questioned by a human refugee) agreed. “But the Pariah lineage of the Necrontyr endure.”
Ch 49: The accomplishment of the two Prophecies about the end of the two rulers of the Chaos Imperiums, in this case, Abaddon. In stead of being killed by the 'Last Good Man' (a scout), he was... spared (mostly due to inrecognation), and carried out of the burning Flagship of Huron Blackheart by the man in particular. He was moved by this. Probably. Thus, Abaddon the Despoiler died, just as Prophercised, but not through battle, but through kindness. Kinda.
The young soldier turned to Abaddon’s prone form. The boy’s face was clean and lantern-jawed, and filled with a righteousness Abaddon had learnt to loathe thousands of years ago.
Was this the last good man? Was this his end? Abaddon watched the scout’s rifle. Slowly, the weapon was lowered.
“Can you walk marine? What chapter are you? Get up, or you will perish here with the Blackheart! We have mere minutes before we strike (as in, crashing into) the craftworld. We must move; now!” the boy bellowed, hauling Abaddon up to his knees. “My name is brother Kelfdon of the Silver Skulls; your assistance was most welcome.”