basically, the vessels presumably have skin to entrap the void inside of them, and to move around. Soooooooo what if a vessel when through the process of vesselfication (is that a word?) had it's skin just ripped off or punctured. They would just permanently be a soul, but still have the mind of a vessel. Its weapon would be entirely spell based, with additions such as something like a soul suck.
idea of making a vessel from @pastry_pets