Who do you guys think win in the end?
Smart Money's on the Nids, but I say Chaos.
If the end times retcon (thanks for ruining my favourite fantasy universe GW) is any indication. Chaos has always won.
Nid's suffer a similar issue to the necrons. They can't touch chaos. They can destroy its agents but chaos itself. Nope.
And the space marine game was planned to be a trilogy. Captain Titus was meant to go with the black templar. Then goes renegade and is followed by those who remained loyal to him. He explores why he's immune to chaos as he thwarts chaos and eventually founds his own chapter.
Frankly I have always thought Space Marine should have been a Grey Knights game. No 40k video game plot ever stops at the first enemy.
The final boss is always freaking chaos in the end.
Oh god no, to hell with the Grey Knights. Space Marines are bad enough.
Also as far as I know Choasy things don't effect the Nids.