I've found that the best way to fix this is to get everyone who participates in the group conversation to delete the conversation from their phones. Then once e

I've found that the best way to fix this is to get everyone who participates in the group conversation to delete the conversation from their phones. Then once everyone's done that, one person can send a message to everyone else and it should use SMS. In my experience, it looks like iMessage stores metadata about the chat medium for a given conversation, and that's determined upon creating the conversation. When sending individual messages, iMessage doesn't seem to attempt to determine whether conversation partner has gone dark from iMessage and fall back to MMS going forward. So everyone else gets the message, but not the person without an iPhone.