https://www.marvel.com/articles/comi...ome-in-x-men-8
Finally, we have to have a talk about Vulcan. The Krakoan Resurrection Protocols have returned him to life, but Vulcan doesn’t seem to recall the events of X-MEN: DEADLY GENESIS (2005) or his subsequent transformation into the tyrannical Emperor Vulcan. Even Vulcan’s formerly dead teammates, Petra and Sway, are having trouble adjusting to their return.
Previously, it was assumed that Vulcan was resurrected this way intentionally, so that he could finally be the third Summers brother without the baggage of his heel turn. However, the ancillary matter touches upon Vulcan’s death in WAR OF KINGS (2009) #6. Vulcan and Black Bolt disappeared into the Fault, but only Black Bolt made his escape. The troubling thing here is that ShI’ar intelligence suggests that Vulcan didn’t die at all. That may be why Vulcan’s Krakoan counterpart seems so incomplete.