I have to re-evaluate my decision after reading the DOW novel Series. let's just say that i believe it won't be the eldar. I think it's going to be either the Imperium, the Tau, or the Necrons.
1. Orks, there main space fleet crashed, and only have afew strangler ships left. Plus gorgutz has a tendency to run and hide.
2. I can't see Eliphas taking control, because even if he wins, and immediate exterminatus would be declared upon the planet.
3. I don't know how much time passes between WA and DC but i don't think the SM will purge the whole planet, if the Imperium wins it will be due to the IG.
4. Well since the Necrons came from within the planet, i don't know whether or not they have a fleet there, but if a fleet did appear it would most likely tip the odd's heavily in there favor.
That or after a victor is decided, is skips immediately into the plot line of soul storm and the war will start all over again.