disowning family

If a family member is really nasty (and has been for years) about an immediate family member and suddenly you find out it's reached another level of nastiness, it's gone too far, what are your thoughts on disowning them? Especially when you always put yourself out and bend over backwards to please that person, you've put your life on hold for them, you have always done everything for them without even a thank you?  If you've been through this was it a hard decision? Did you manage to stick to your guns or did you gradually rebuild it over time? Do you regret that decision?