I don't get iMessage

Imagine this scenario: I have an internet-connected iPhone, and I want to text a friend of mine who is on the road. His iPhone has mobile data turned off, but his iPad/iMac/second iPhone is in his house, connected to the internet. What will happen then? Will my text be sent as an SMS directly to his iPhone? Will it be converted to an iMessage (since one of his devices is online) but he will not receive the message as he is offline? How is it planned out?