Addendum: apparently that motto should read "eithe diamenoien hoi hetairoi," (long live the Companions) which I think sounds all right poetically but is in my humble opinion less suited to bellowing. But I think that Meg Anassa is correct that it ought to be an optative of wish rather than a third person imperative (isn't the idea of a third person imperative weird?), so there it is. And "eithe diamenoien hoi hetairoi" sounds better than "diamenoien hoi hetairoi" or "ei gar diamenoien hoi hetairoi," all of which mean the same thing.