The following advice if for the mk1 (not sure if it applies to the mk2) and is all 'IIRC', as it's been a few years since I sold my mk1 Focus, so you might want to wait for someone else to confirm it before acting on it...

Does the key still start the car ? If so, this indicates that the immobiliser transponder chip is still working, even though the buttons no longer work.

You need two working keys (that start the car) to program a third to do the same yourself, so if his remote key still starts the car and he has a spare (working) key then, AFAIK, he should be able to buy the remote fob part of the key (£40-50 online), attach it to the key part of his old remote and program it himself without needing to go to a dealer.

Details of how to program additional keys are in the Focus manual.

If it's not possible to switch the key part from the old to new remote quick enough during the procedure, then blanks are available fairly cheaply and getting one cut shouldn't cost too much.