Given the resurgence of the Necrons - what do you suppose would happen if more than one Craftworld went to war against them (perhaps to prevent the awakening of another C'Tan) and each brought there Avatar?

Since they are both fragments of Khaine - would they join together and form a super avatar? Given the nature of gods in 40K - seems like a reasonable outcome. Perhaps getting all the craftworlds to bring there Avatars out would create a being powerful enough to destroy a C'Tan for good...

Anywho, just a thought.