Now that the Jailer is defeated and the Helm of Domination has been broken and reforged, wouldn't Death Knights lose their eye glow?
It signifies domination. Back when Arthas' helm was removed and he was defeated, he came back to his senses and lost his eye glow. When Anduin returned to his senses, the blue domination eye glow faded away. When Bolvar's helm was removed and so did his eye glow, he pretty much became old Bolvar and less Lich King.
Wasn't it an indication of their mental connection to the Jailer, or in the case of playable Death Knights, to the Lich King?