Tiramisu,
I'm not sure I understand - where will the difficulties lie in WW in providing the service on say a standard JFK flight?
Bearing in mind it's still a minority of flights with IFE problems, the product has been reduced, and the CSD is there to man a trolley to fill the gap of the lost crewmember.
Worst case scenario as I see it is that the crew rest will be reduced marginally. (No hardship on the Bombay I did last week when half the crew were in bed 1.15 after take-off)