If Rogal Dorn died in Sanguinius's place

What if Rogal Dorn boarded the Vengeful Spirit and died instead of Sanguinius?

Sanguinius's survival could deprive the Palace defense of the Blood Angels' mass Black Rage, while Dorn's death would alter the Imperium's later institutions and leadership.

In this scenario, Dorn dies aboard the Vengeful Spirit in place of Sanguinius after directing the defense of Terra. Sanguinius's survival would prevent the mass Black Rage that drives the Blood Angels against the attackers at Eternity Gate, creating a risk that the Palace falls. Dorn's death would also remove later arrangements associated with him, including the Last Wall, knowledge of the Dark Cells, and his part in making post-Heresy reforms possible. The Imperial Fists' likely response is disputed. Sigismund's description of their mechanical behavior when Dorn is badly wounded is read either as evidence of their reaction or as questionable characterization. If the loyalists survived, Sanguinius could provide a unifying figurehead while Guilliman concentrated on administration and reform. Their earlier partnership in Imperium Secundus supplies the model. The different contributions of a figurehead, a campaign commander, and an organizer remain central to the counterfactual.