The people with iPhones are still Apple's customers, and it's their messages that are disappearing. That's a perfectly good case for a CAL.
Suppose that someone tried texting someone for medical assistance (silly, I know...), and that message was not delivered because the recipient changed their phone but kept their number, is that the fault of the person that changed their phone or is it the fault of Apple for not being able to realise that people might someday want to change devices?
Suppose that someone tried texting someone for medical assistance (silly, I know...), and that message was not delivered because the recipient changed their phone but kept their number, is that the fault of the person that changed their phone or is it the fault of Apple for not being able to realise that people might someday want to change devices?