Highspeed,
Now with the books in front of me, I see you dilemma....
In Volume 2, it is stated that,
"The main AC electrical power sources are :
-left and right IDGs
-APU generator
-primary and secondary external power."
BUG is discussed in a seperate paragraph, and no mention of it being a MAIN AC ELECTRICAL POWER.
In the QRH,
"There are some situations which always require landing at the nearest suitable airport.......
-one main AC power source remaining (such as engine, APU or backup generator)
......."
So therein lies the confusion, but if I am in the situation that you have mentioned, I would play it safe and land at the nearest suitable airport.