Ah finally. I visit 2 Forums this one and a GW forum (Warseer) so now I get to talk about my other hobby
. First, the Emperor will never die completely as that would ruin the whole setting. As for being able to stand up against the nids I have one word, Commisars. One of the main ideas of command (at least in some circles) is to fear your officers more than the enemy. So it's a case of fighting the Tyranids or to use secret 40K talk, being found wanting.