If there was nothing I could do to win the war I would have accepted defeat and become a powerful vassal of the King of Scotland. Then I would build up relationships with fellow Irish vassal (who most likely dislike their new liege) as well as Scottish vassals who for one reason or another also dislike their King (being so young he probably don't have that good a relation with them). Then I would try to get an alliance with someone outside the realm through marriage. Then start a plot and bide my time... Once the Scottish king has gotten himself into some sort of trouble I would strike and take back the crown. Revenge and grudges carried for generations is what this game is all about 