Lord of the Night might also have proven that he died, I mean the novel is all about Sahaal getting an item to solidify his right to lead the Night Lords after Night Haunter's death. Other characters go on to talk about how Sahaal is not supposed to lead, they are; why would any of them be thinking they are going to lead if their primarch is still alive?
Also, Zso Sahaal was trapped in a warp storm/stasis lock for the better part of ten thousand years, not a mere century or two.
Also, Zso Sahaal was trapped in a warp storm/stasis lock for the better part of ten thousand years, not a mere century or two.