I suppose it's time to tell you as much of the rest of the story as I can. While I had originally intended to present a story in which you never quite knew whether or not the Accusers existed, I mucked that up in telling the Homecoming story. It was such a compelling vignette, though, that I couldn't resist telling it and spoiling the secret.

Yes, the Accusers existed. They were created in the 2nd Founding and were one of the Primogenitors. While many of the members of the chapter may have been inducted at the tail end of or after the Horus Heresy, perhaps serving during the Scouring, the senior members of the chapter were veterans of the Great Crusade and the Horus Heresy.

Led by Astinax Megaeros, a chapter master in the Ultramarines Legion and first (and only!) Chapter Master of the Accusers Chapter, the Accusers embarked on the core mission of the Scouring: pursuing and destroying the traitor legions. They participated in the combined action of multiple Ultramarines Legion successors at Tsagualsa. After the apparently mortal wounding of Roboute Guilliman by Fulgrim and the subsequent placement of the former in stasis upon Macragge, Megaeros, utterly devoted to his gene-scion, led his chapter in a crusade against the traitor legions. Slowly, Megaeros descended into an existence of wrath and hatred, the majority of his chapter willingly following his lead. Eventually, however, some members of his chapter resisted and the chapter was broken by a schism. Megaeros and his followers were defeated, though we don't know of Megaeros's fate.

The mystery, then, is why we've never heard of this chapter; and what became of the loyalists.

The answer in my mind is that the Ultramarines and their Primogenitors are not as squeaky clean as many suspect, and that they, too, are capable of subterfuge and deception. In this case, the Ultramarines and their successors decided to pretend as if the Accusers never existed, destroying all evidence to the contrary. The code word for this is the Corrigere Sanction, whose meaning is known only to the Primogenitors (including the Ultramarines Chapter). This means that any records of the Accusers' existence were either destroyed or hidden away. Yes, this throws the pedigree of the Apocrypha of Skaros into question (though the official expansion of the 2nd Founding, which happened after I created this chapter, has already done that). Just as the Unforgiven chapters hunt for the Fallen, the Ultramarines and other Primogenitors follow the Corrigere Sanction in concealing the existence of one of their own falling to Chaos. From an in-universe perspective, the fall of the Accusers would be only the first of multiple scions of Roboute Guilliman to fall to Chaos over the millennia, but it was a traumatic event for Guilliman's sons at the time.

For what it's worth, the sword described in the Homecoming story, which was presented to Astinax Megaeros by Roboute Guilliman upon the chapter's founding, was recovered and returned to the Ultramarines. That sword is now known as the Talassarian Tempest Blade and is currently borne by Cato Sicarius, the Commander of the Victrix Guard. How that sword returned to the Ultramarines is not my tale to tell.

I previously mentioned that the Accusers present me with a ready-made chapter if I ever do a force for the Scouring. Knowing that some of them fell to Chaos, it should be obvious that the Accusers also present me with an opportunity to create my own Heretic Astartes warband, perhaps even one that operates during the Era Indomitus.

I had an idea when I first started working on the story, but I was approached by another member of the B&C community who had an idea for a DIY chapter that meshed quite well with what I was working on. We decided to combine our efforts. No, I won't tell you who that member was, nor will I tell you the name of their chapter. It has been over a decade since I corresponded with them, but as far as I'm concerned, the intertwined story that we collaborated on remains as valid now as it was over a decade ago. The tale of what happened to the loyalist Accusers, whether or not they still exist in the Era Indomitus, and what they've been up to over the intervening millennia is theirs to tell.

This whole idea was an interesting exercise. The return of Roboute Guilliman to the Imperium creates risk for this DIY, however. After all, the Primarch almost certainly remembers Astinax Megaeros and the Accusers Chapter; and he most likely recognized the Talassarian Tempest Blade wielded by Cato Sicarius as the weapon he once bestowed upon his devoted son. Would Guilliman seek answers from the Ultramarines, who likely have the records hidden away deep within their librarium? Would the Accusers be reborn as a Primaris chapter in the Ultima Founding? Or should I just consider this one of those fan-fiction DIYs that can't exist as true "canon" since the official lore ignores them, implying that they never existed? Or should I entertain the pipe dream that GW might some day incorporate the Accusers into the official lore (I won't hold my breath )?

But really, what happened to the loyalist?