It currently says on their website:
If you fail to check in at all for your flight from the UK, we retain the right to cancel any other arrangements you have booked with us and you will be unable to use your return flight to the UK. No refund can be made for any unused arrangements.
Just also checked with TCX ground staff at BFS, the passenger thats travelling out a day later need to show himself at checkin with his documents in order for them not to cancel his return to the uk. Otherwise pop into the TCX/Handling Agent a day or two before hand.