A B767-300 GEN DRIVE warning annunciated during an oceanic crossing. The QRH checklist did not address double GEN DRIVE failures and suggested subsequent crew action.

Narrative

Approaching 50W west bound we were alerted with 'R Gen Drive'. The QRH had us disconnect the generator and start the APU. No problem. We're still a two power source operation and good to continue to destination (though I would have preferred the checklist have me start the APU first before I disconnected the drive). Now you start asking 'What if...?' What if the other Gen Drive quits? What if they were serviced with the wrong type oil and it's only a matter of time before the other one quits? The QRH only addresses 'Gen Drive L or R' not 'L and R'. If you elect to run the Gen Drive checklist a second time you have now eliminated both generators. Looking at the 'Gen Off' checklist or the 'APU Gen Off' checklist you find a note advising to avoid IFR and land at nearest suitable airport... but no such caution the 'Gen Drive' checklist. Granted one must fail to connect the dots; but on a dark and stormy night with one guy flying and talking while the other guy; maybe new to the airplane; reads the checklist; it could easily reach up and bite you. It would seem that a similar note or caution should be included in the Gen Drive checklist.