Kosh says to him, "They are a dying people. We should let them pass." Sinclair asks, "Who, the Narn or the Centauri?" Kosh simply answers, "Yes".
I always took it to mean that both the Narn and the Centauri were screwed
This was the first B5 episode I ever saw, and it so blew me away that I was converted at first sight. And the scene that clinched it for me? The one where G'Kar has his Dust enhanced vision and is informed by Kosh that some must be sacrificed so that all may be saved. It still sends a shiver up my spine.