According to wowhead, this raid is pretty non-linear after the first two bosses, you could kill two more bosses and bam, you can move on to carapace of N’zoth and N’zoth. I bring this up as I assume that Wrathion tearing into N’zoth with Xal’atath is important but in order for Wrathion to get the pointy dagger, you must kill Dark Inquisitor.
Has anyone actually tried this in their raid? I assume you must actually kill the first two bosses and Dark Inquisitor and Vexiona (or two other bosses on the other branches) to get to N’zoth.