So far in the heresy, Night Haunter and Sanguinius have used their prophetic gifts to accomplish things. From knowing the next sword thrust, to repelling demons.

While it can be argued that a lot of the prophetic visions are sent by chaos to sow doubt (Horus's for e.g.) They have seemingly legit probability forecasting. Both have agreed that the Emperor, considering their gifts, can read the future and past at will.

The emperor stated in the outcast dead, that he knows what's coming with Horus, and he knows what will happen to him and he has to accept it as his fate.

What I don't get is if he knows exactly what's coming, knows what would have been the end result of his dealings with, and attempting to betray the Chaos gods, why did he take that path ?

Did he think for a moment that he could have won ?

Everyone from the Eldar to the alien coven knew what was coming, I refuse to think he didn't.

Unless he thought the alternative was too terrible to even allow.

So he chose this particular path, now that the heresy is upon him, why go fight Horus ? Why not nuke him from space, why not do anything at all but the very thing you eventually do ?

Unless the current state of the Emperium is the best option for the survival of humanity and it really was the lesser of all evils (as shitty as it is now)

Poor dude.