Wouldn't the public announcement of “So-and-so is no longer one of Jehovah’s Witnesses” be grounds for defamation? Given almost all members of the JW community universally associate this phrase with the person having done something bad, or being of bad character, and as a result would shun that person. It's equivalent to saying “So-and-so is of such bad moral characther that they are no longer one of Jehovah’s Witnesses, and you should all shun that person”
If I said “So-and-so is a lousy person” in front of an audience, that would be enough grounds for a defamation case.