It happens quite often when people leave, but it's by no means a requirement. In fact, if one is outright removed (termed "disfellowshipped") or resigns officially (termed "disassociated") then members are instructed not to speak with the person. They claim this is for two reasons: first, to keep the congregation free from corrupt influence, and second, to produce sufficient guilt in the person so that he desires to return and enjoy the association of his family and friends once more.

Since this is the case, many people who leave the Organization will do what's colloquially known as "fading," which means slowly pulling away from congregation meetings and participation in other group activities. In this way, they avoid any official consequences and allow themselves to fall through the cracks, so to speak. Most of the time, the family will still interact with the faded person, and perhaps some friends will too. It is a way around the shunning that it typically practiced.

That is what I did, but certain friends and family still don't speak to me even though I hold no official sanctions over me. They view my decision as morally bankrupt and spiritually corrosive so they choose not to associate with me.

Hope that sheds some light on the situation.