Yeah this theory is mostly wishful thinking. With Vulcan though I think he might come sooner because five out of the nine relics have already been found with three in the Salamander regents possession and the other two are in the home fortress, so it possible that Vulcan come back earlier then expected. I also agree that the traitor Primarchs will try and beat each other to Guillaume first but if more loyalist Primarchs start returning then they might have to work together to kill the Primarchs. I think it would be just bad ass is Jagathai Khan just walks out of a dark Eldar webway chasing dark Eldar who are trying to run from him and then he just shoves his boot straight up their ass.