No, they'd re-price the ticket as flown, as a one-way, and you'd only get back any difference between the one-way and what you originally paid, if it even allows refunds after departure. Too obvious of a loophole.
You could re-use the value (likely half of the r/t) for another segment, it has to originate in the US, but I don't think it has to go to CAI, can probably use to anywhere in EMEA although the ticket would still be re-priced as two half-round trips based on fares at the time of original purchase.