Originally Posted by Angel of Blood
I don't think they would because they all would have fallen at different times and for different reasons imo. The Night Lords were already on the way out before the Heresy kicked off, and they weren't all jumping in to help them then. The Thousand Sons would have fallen against their own choice. The World Eaters would have been taken out before they rebelled i think. And the Iron Warriors, well they would have taken quite some time i think, or would have been sanctioned or called to account for their actions after Olympia.
The Night Lords, Thousand Sons, World Eaters and Iron Warriors were all on their way out when the Heresy started. The only reason they weren't called to account for the various things they'd done wrong was because they're was a bigger fish to fry.
The Night Lords were pretty much rogue after Night Haunters attack on Dorn and the destruction of Nostromo.
The Thousand Son were being sanctioned and Tzeetch would likely have had them team up with the other some how.
The World Eaters were going to be called to account for that massacre the Ultramarines witnessed (don't remember the name). Where it specifically states that the Heresy broke out before that sanctioning could come.
The Iron Warriors massacre of Olympia would likely have seen them outed. If not I think one of the others could have persuaded Perturabo to join them (I went it why on another thread).
Others who might have joined them included Fulgrim (under Slaaneshs influence), Lorgar (he was already the gods pawn), Mortarion (still don't really know what was going through his head), Alpharius (again, don't know what his thought process was), the Lion (it's certainly a possibility, he was arrogant, paranoid and distant and the gods are noted to have taken an interest in him). So really all that changes is that it becomes the Lionite Heresy and possibly succeeds (although it doesn't sound as cool).