It's possible, but thinking of Sargeras in terms of the Titan physiology covered in "Chronicle" I don't think that would even be physically possible. "War of the Ancients" maintains that Box essentially nicked Sargeras before being skewered on the edge of his sword Gorribal, but if a Titan truly is close to the size of a planet then that nick would be the equivalent of normal human dragging an axe along the ground - and Gorribal wouldn't have skewered Brox but crushed him into meat-paste long before it's edge ever came into play. I think it more likely it was simply an avatar Sargeras was going to use to pass into Azeroth through the Well of Eternity's portal (which also wan't planet-sized or else it would've eclipsed the entirety of Azeroth itself).