Yeah ... OTOH he makes an appearance as a dream-figure in III.6.1, and I have the feeling that we will eventually get the chance to give him his just deserts. A la mode. Looking forward to that.
Now that he, and the Falcon clan, have thrown in their lot with Saruman, they will likely take part in the big battles to come. I can see us running into Lheu Brenin in the middle of a big battle - be it at Helm's Deep (if we are there), or the Second Battle of the Fords of Isen (if we are there), or any other battle inbetween - and will then be given the chance to have our revenge. Getting to battle an old enemy one-on-one, while battle rages all around you, it sounds almost like something out of a movie-script.