Not at all. Beyond the technical problem (mutually assured destruction is dependent on having access to weapons of mass destruction), medieval warfare was, as a rule, limited in scale, scope, and aims. The objective was almost always to compel the other side to do what you wanted (give up a piece of land, allow your candidate to succeed to a disputed inheritance, etc.), not to effect their ultimate destruction. Almost all of Clausewitz's theories are inapplicable, but when he said that "war is the continuation of politics by other means," he was dead on the money.