Family members are often seen as people who have each other's support no matter what. This is an idealistic approach, but it works for numerous people. However, it is not realistic or even healthy for others. There are people who are estranged from certain family members or their entire families and with good reason. Contrary to popular practice, there is nothing wrong with ceasing communication with a family member. Some people simply are not worthy of familial relationships. In these cases, it is okay to stop talking to a family member without feeling guilty.
If a family member is a violent criminal or you simply disagree with their criminal behavior, it may be time to stop talking to him or her. This is especially true if the crimes are committed against yourself or another close family member. When a family member's criminal behavior extends to you, you may feel uncomfortable or even afraid around him or her. It does not matter that they are family, if they make you uncomfortable or scare you; ceasing communication with them is completely within your rights. Of course, the criminal behavior does not have to affect you for you to have valid reason to feel uncomfortable.
Unfortunately, people are capable of doing some rotten things to each other. Family or not, people are people. They may betray you, use you and any number of other horrible things. There is no reason to continue talking to someone who is mean to you. No one is obligated to remain on good terms with anyone else. In your life, you are in control of who you want in it. Life is too short to deal with nasty people simply because they are family. The level of nastiness you are willing to deal with is completely up to you.
Whenever You Choose
There is no set of criteria for maintaining contact with family members. You can choose to stop talking to a family member for any reason, at any time. The reasons mentioned above are good reasons, but, in reality, you do not need a good reason. Your family is your family, just as your life is your life. Live it how you see fit and surround yourself with people you like talking to, not people you feel obligated to talk to.
In the end, you always have the option of reconciliation with any family member, if that is what you want. Therefore, if you want to stop talking to a family member, you should not feel like it is forever unless either of you want it to be. Sometimes it is just healthy to take a break. Other times, it is healthy to forget that family member ever existed.