Comment by maram

>>If Leave this Conversation is grayed out on your iPhone, there are only three participants in the iMessage conversation, and you can’t convert a three-person iMessage conversation to an iMessage between two people. >> Even if you delete the entire conversation from your iPhone, you will be added back to the group the next time someone sends a message. The only way to leave a three-person iMessage conversation is to add someone else to the group so it becomes a four-person conversation: Then you can leave.