Blizzard Entertanment posted a Shadowlands short story titled We Ride Forth — by Robert Brooks. This short story features Nazgrim, Thoras Trollbane, Sally Whitemane, and Darion Mograine. The Lich King’s Four Horsemen, travel to Icecrown, hoping to ascertain their master’s inscrutable plans, and put an end to them if necessary.
The story starts in Acherus, hovering above Suramar, in the Broken Isles. Seems the short story serves as a preamble of when the death knights felt the sudden absence of Bolvar the Lich King’s thoughts. Presumably, because the Helm of Domination that granted him that ability was shattered by Sylvanas. The story serves as a platform to let us know what happened from their point of view and their reactions to the abrupt disconnection between Bolvar and the death knights.
This story has some twists. The death knights did not come to Icecrown to help Bolvar, but to kill him. As you read, you will find out things that we haven’t found in-game.
Bolvar the Lich King had used the Helm of Domination to control the four horsemen against their will. It is revealed that Bolvar forced them to help against the Burning Legion at the Tomb of Sargeras, and that he forced them to raise corpses into Death Knights. Seems Bolvar somehow knew in advance, or at least sensed that Sylvanas was coming. This kinda matches with continuity seen in World of Warcraft: Arthas — by Christie Golden. Arthas was able to envision future events before his eyes.
So whatever Bolvar might have seen, he commanded his horsemen against their will to bolster the Death Knight numbers for what was coming in the near future.
Something I found interesting is that Acherus traveled to Kul Tiras, Zuldazar and Darkshore to collect the corpses of those who died with honor to raise them as Death Knights of the Ebon Blade. This immediately tells me we might see familiar faces (who we know died during Battle for Azeroth) return as Death Knights.
You can read this story online and/or download it in PDF format. It’s about 4 pages long.