B767 First Officer reported electrical malfunction resulting in a single generator configuration inflight. Flight crew diverted and landed uneventfully.

Narrative

On Day 0 Aircraft X [requested priority handling] for electrical malfunction that occurred during the climb to cruise altitude from ZZZZ intended for ZZZ. The nature of the problem was a single generator source of electrical power due to the APU generator coming offline and a previously deferred left generator Inop. An uneventful diversion and landing was completed at ZZZZ1 with no damage to aircraft or crew and no other injuries reported. Although this was an uneventful outcome several known threats were not briefed properly or mitigated which resulted in errors that were late or unrepairable before the event.I believe that the breakdown for Flt XXX started the night before with Flt XX ZZZZ-ZZZ. After starting both engines we had LFT Gen ICAS message with a negative response with an attempt to reset. Maintenance was contacted. The issue was MEL'D and a new maintenance release was created. The Captain took the position that the flight was conductible under the MEL and that he was Okay with the Aircraft. I stated my position that the flight was conductible under the MEL but was that the best prudent decision while operating at night across the ocean with 200+ passengers and crew; when we were at a significant Maintenance facility and major world hub that could accommodated the passengers with high regard. I also stated I would error on the side with conservativeness as a default. The flying FO (First Officer) stated he sees both sides of the discussion; but too would also error with conservativeness. The Captain restated his position about continuing with the flight and pressing on. I then reinstated my position about having further maintenance inquire into the matter for we don't know what exactly what is happening with the Aircraft and that I was Uncomfortable" with conducting the flight with Passengers on board. Flight was cancelled.Day 0 Flt XXX ZZZZ-ZZZ was conducted under the MEL as a Maintenance Ferry Flt. Van pick was XA55 with a XD00 departure. Arriving at Operations seemed there was confusion on if or not we were conducting the flight. Coordination for transportation to the hard stand was made. Upon arriving at the hard stand there was no Aircraft. Approximately 2 hours later the aircraft arrives. Waiting on Maintenance to accomplish ETOPS inspection and finally completed we board the aircraft well beyond our XD00 departure time. There was much discussion about our trip but a lack of full briefing occurred in many areas. After starting both engines the APU was shut-down; lack of fuel balance awareness caused a departure with a fuel imbalance; this was all impacted by a runway change at the last moment for departure (XXC to XXL) which shortened the taxi time by a significant amount of time which possibly would have allowed for the identification of Errors with the ability to Repair. It seemed like a sense of need to depart which wasn't the case; seeing that we had already exceeded our departure time by approximately 1hr+ and the fact we were only a Maintenance Ferry. The aircraft departed in a Single Generator configuration which caused the proper load shedding of both L & R Utility buses. Once in flight the APU was started; however the APU generator came off-line after attempting to reset both Utility buses. The APU generator was never recovered after several attempts. The Captain called Dispatch and Maintenance Control and coordinated a divert. After coordinating with Dispatch/Maintenance Control the plan was to divert into ZZZZ1 and [request priority handling] due to Single Generator operation. Approach and Landing and Taxi to the hard stand was uneventful."