Let's play hard ball.... let's say a new light appears !
1 Cor 5:11 ...."you must not associate with somebody with claims to be a brother or a sister....but is a sinner, etc etc."
So if somebody claims NOT to be a sister o brother anymore.... let's NOT shun that person! That person is like a worldly person again and we don't shun them, we just use common sense. Problem solved.