Luther and his part of Dark Angels are now explicitly defecting from the bad guys, not the other way around.

It's believed that he was killed by Dorn, by then a Daemon Prince already.

Perturabo ( presumably) gets killed at some point after the Heresy.

Mortarion dies fighting the Emperor, but damages his armour enough to let Horus land a hit later.

It resulted in Raven Guard turning into 'winged nightmares'.

Deal with the Devil: Corvux Corax had to make a deal with Tzeentch to help rebuild his Legion.

Dark Lord on Life Support: The Emperor was put on the Black Throne after the failure of Heresy, and now Lorgar tries to spill enough blood as a sacrifice to Chaos to make him ascend as a new Chaos God.

The Corruptor: Lorgar made the Emperor vulnerable to temptations of Chaos by telling him that he can better protect Mankind if he becomes a god.

It results in Alpha Legion and Thousand Sons attacking them first.

Cavalry Refusal: Ultramarines don't bother with going to aid the Emperor on Terra, preferring to wait till both sides weakens each other, likely with intentions to finish off the survivors.

and sides with Horus, resulting in imperialists being massacred, and only escaping due to help of traitors amongst rebel forces, who provided them with one of their ships. The rest of forces (Dark Angels, Night Lords, Iron Warriors, Alpha Legion) attacks next.

Cavalry Betrayal: The first three Legions to attack Horus and his forces on Isstvan V (Sons of Horus, Death Guard and World Eaters) are Iron Hands, White Scars and Raven Guard.

The Cavalry: Due to successfully dealing with Space Wolves attack on Prospero, Thousand Sons manages to assist in defending Mars, arriving just in time to stop the imperialists from releasing the monstrosities hidden deep below.Horus saves Perturabo when he's about to be killed by Sanguinius during Siege of Terra.Attempt to corrupt Horus on Davin still happens, but it fails due to intervention of Magnus, Curze and Alpharius, who are now aware of dangers of Chaos.Those who never dealt with their rage (like Angron himself), have leaved to the Eye of Terror to continue fighting Chaos. Unlike canon, they never fully embraced massacre for the sake of massacre, and, after the Heresy, ditched using the butcher nails completely (and even managed to remove the ones already installed), specifically to not repeat the fate of Blood Angels, in whom they saw their possible future if they would allow their wrath to overwhelm them. As in canon, World Eaters still used butcher nails, with all the 'nice' effects on their sanity.

More sane ones followed Sigismund and turned Black Templars, while others turned Khorne worshippers and formed Crimson Fists. The Imperial Fists have fractured after the Heresy.Under Sanguinius, the Blood Angels fell to Khorne and became mindless berserkers, spilling blood for their Blood God.Batman Gambit: Horus lowers the shields of his flagship, Vengeful Spirit, expecting that the Emperor wouldn't resist temptation to slay him personally.They managed to rebuild and eventually even create successor Chapter (Black Hoods) only by M33 (though in this fic, Chapters are ten times bigger than in canon). Back from the Brink: There were 80 000 Salamanders before the Heresy.It's believed that he's wandering around the galaxy, trying to redeem himself. The Atoner: Luther has leaved after the Heresy, receiving way too much blame for failing to show up for Siege of Terra.One of them was cut by Jaghatai-Khan himself, who's now a Daemon Prince. An Arm and a Leg: Abaddon had lost both hands, replacing them with bionics.Arch-Enemy: Raven Guard (who became Tzeentch worshippers on their own initiative) are now mortal enemies with Night Lords, and frequently clashes with them.

Tv tropes horus heresy