There has been only one breach-of-treaty excomm, namely of Carillon for assassinating a Komnenos. But he wasn't at war and seems to have weathered the effects reasonably well. Before that, Frosty also killed a Komnenos heir while we had a NAP, but that was settled by compensation, with no excomming. (In hindsight I should have gone for the excomm and DOW, and taken back the Levant; c'est la vie.) That said, nobody is arguing that Jakalo shouldn't have been excommed, had he declared war on Frosty; that was always perfectly clear. The question is whether he would have, or should have, acquired a lot of human badboy for breaking a promise.