swiss_swiss,
All things being equal, I agree. But I have personally seen a failure mode where a dead phase on a bus was supplied with enough voltage to keep the genny / bus from tripping off, via the two still live phases powering an electrically driven hyd pump. A generator and a motor are essentially the same thing - you spin a motor with a dead phase, and it will generate on that phase and feed any component connected to that phase on the bus. Frequency lockout wouldn't necessarily pick it up either, if the remaining 2 live phases of the motor could draw enough juice from the bus to keep it spinning at close to its normal running speed.
Make sense, or am I not explaining this very clearly? Just to clarify, this isn't idle speculation, this has actually happened to me (on another type, considerably older than 777)