I just read an excellent article on parental alienation by Dr. Katherine Andre. She examines whether children who experience parental alienation ever reconcile with the alienated parent, finding that 95% of children do and only 5% do not. Dr. Andre lists four factors that are important in making the difference:
One is contact of any kind, such birthday cards, graduation gifts, or the occasional phone call, even if rebuffed by the child. Second, of course, is love, love, love. Dr. Andre stresses that it is important not to try and defend or explain yourself, unless asked. The primary message to send the alienated child is that you love them. (My comment: It is important to remember that they are being deluged with the opposite message.)
I agree with this wholeheartedly, based upon my own experience. When my parents divorced and my father left, leaving me to live with my mother, I heard an almost non-stop barrage of negative comments about my father. When I was with my dad during his parenting time, however, he said nothing about my mother (except for one isolated incident I can recall). By declining to jump into the fray, my father gave me the freedom to reach my own conclusions about "who did what." He gave me a calm space from which to see the whole picture. That was a godsend to me, since my mother was adamant that we take "her" side and conclude that my father was no good. It may be heard to believe, but by remaining neutral, you are a more powerful advocate than you could ever be by trying to convince your children of your "innocence." Without my dad's neutrality, I don't believe I would have recovered from the alienation that was ongoing in my teenage life.
Dr. Andre lists community support as a third factor in children's recovery. There wasn't much of that going on when I was a child. The fourth and final factor is hope. Always keep the door open, even though it is painful to be rejected by your own child (and you are human and have feelings, like anyone else).
Understand that the alienated child, however they may behave, has a deep-seated need to love and interact with both their parents. By keeping the door open, you maintain a lifeline of love.