My experience has been that a refundable ticket is refundable if it isn't used to actually fly somewhere. You can purchase a ticket, check in, get to the gate, not get on, watch the plane leave, go home, wait a week, and call up and still be given a complete refund.

When I last needed such a refund the people at the checkin desk told me to just go home and call to claim my refund. They didn't seem interested in processing it for me on the spot. I should note that it's also polite to tell the folks at the gate to remove you from the flight if you know you won't be on it.