As Tarvek put it...
THIS! WAS! NOT! MY! PLAN!
I think Tarvek would be pretty sad to learn that he wasn't the Storm King. While he's a lying snake, he definitely seems to believe in the whole Storm King mythology and the belief that having the Storm King ruling is what's best for Europa. Zola and Gil's debate over the Pax Wulfenbach made it pretty clear that not everybody is happy with it, and it was pretty much a case of "he's a tyrant, but a pretty benevolent one and this is better than anything else".
Also, given the stink over resurrection I think having some long-dead guy brought back via mind transfer might not work as well as you might think. The nobles would likely reject the ancient Storm King in a way that they wouldn't for his legitimate descendant.