Sorry, have to disagree. Would you consider your sister any less than a sister after she married - even if you didn't like the match?
But I know it might me true. Both my parents were cut off from their families for marrying each other. It took 20 years of marriage for them to realize they were wrong
Plus Sirius - cast out for rejecting the notion of pure-blood. And Percy, for casting out his family for not taking the official position on the ministry.