Am in an internet cafe in BKK so can't check but I have a feeling that the center FCC may be powered from the left AC normally but if that is not available then it automagically switches to the right AC...I therefore humbly submit that you will have the center and right A/P available after a left AC bus failure.
It would seem rediculous to leave such an otherwise well sorted, ETOPS approved, aircraft having to be handflown after such a simple, singular system failure.
Or am I remembering it wrong?