@TykiIgnore Snarfulblast, don't make a Hive Fleet. That would end the roleplay REAL QUICK.
Regardless, I was planning on you guys being stuck in the bunker attempting to hold off the forces of Chaos. Currently the Daemon are spawning in, and as such all your chars are in danger. Considering some of these Daemon will belong to Tzeench, a psionic Null would be quite useful in preventing everyone from dying.
@SnarfulblastThe problem with killing Valentus is that his gear is high-tech as shit. His armour is tough enough to withstand a small nuclear blast (that can literally happen in the boardgame), and his weapon is strong enough to crush tanks in one hit. And the Grey Knights are well known for being impossible to corrupt. So really, it's a matter of tiring him out, and he has the stamina to go on fighting for a week without rest.