Honestly, we'd have to see what happens when they finish the Horus Heresy. Considering the story for the HH has changed with the publishing of the current books, who knows how they may end it.
We know the overall story, and the overall ending, but the devil is in the details.
What if they change the final battle to Sang turning against the Emperor and attacking him with Horus, which resulted in the Emperor being beaten like he was. Or even better, that Sang kills Horus and becomes the Champion of Chaos and that cause the Blood Angels to have the Red Thirst and Black Rage.
Maybe they do something with the Lion to set up his return, this is my personal favorite idea as they are giving quite a few books to the Dark Angels when they had very little to do with the Heresy.
If they keep the close of the HH to what we already know, they may move into the Age of Apostasy. This time period helped mold the Imperium into what it currently is.
If they alter the ending in a meaningful way then we could actually see an advance of the plot.