Following the events of the Shadowlands epilogue, Bolvar and Darion discuss the Helm of Domination, Scourge, and Frozen Throne.
Story Spoilers Ahead. Bolvar: Without the Helm of Domination to control them, the Scourge roams leaderless. Nothing remains to temper their aggression. Darion: Indeed. The mightiest among them already vie for supremacy. Like vicious warlords in the wake of their king's death. Bolvar: We cannot allow any of them to seize command and unite their forces. The Ebon Blade must remain vigilant. Darion: And so we shall. Though Azeroth may never truly be rid of the Scourge, we will keep them in check. You have my word. Bolvar: Icecrown Citadel remains a seat of dark power. We must not let it fall into enemy hands. Perhaps I should return to-- Darion: No, Bolvar. Let the Frozen Throne sit vacant. The Knights of the Ebon Blade will safeguard the citadel in your stead. Taelia needs her father. Bolvar: Darion… thank you. Strange, is it not? We both lived lives of service, and even after facing death itself, we still feel compelled to serve others. Darion: Sometimes the greatest act of service is to be present for those who need us. Until we meet again, Highlord.Darion, the current leader of the Four Horsemen, served Bolvar directly during his rule as the Lich King. In the short story We Ride Forth, we learn that Bolvar tricked the Four Horsemen into thinking he was succumbing to the corrupt power of the helm so they'd be goaded into planning his demise. Bolvar hoped that the Four Horsemen would unite and take down whoever won the duel with Sylvanas and donned the Helm of Domination, but was not prepared for Sylvanas to shatter the crown. Here we see Darion convince Bolvar that he does not need to return
Read more on wowhead.com