Air carrier pilot reported during cruise flight and while on break the aircraft experienced an Integrated Drive Generator message resulting in the flight crew returning to the departure airport without coordination with the Relief Pilots on break.

Narrative

Before the flight we noticed they were working on the IDG (Integrated Drive Generator) from an inbound write-up from the previous flight. I noticed in the remarks for the flight that MX (Maintenance) was doing an engine run which we assumed had to do with the IDG write up. We were told the IDG had been serviced and signed off upon arriving at the aircraft. I was working as the Relief Pilot in the first seat. Prior to pushback the Captain requested of MX to send someone to speak to about the IDG fix. She spoke with someone that said they were the lead MX on the fix and that oil had been added and the engine run had been required and ultimately signed off. We all questioned as to where the oil went and the need for the oil refill. The lead mentioned that on an ETOPS check sometimes it is necessary to add oil to the IDG's so we all felt it was a normal procedure. We departed soon after. In reference to the actual divert to ZZZ for the IDG message coming back up; I unfortunately do not have much information at all as we were never advised while myself and the other Relief Pilots were on break. I woke up from break at some point and noticed I had a pairing change e-mail. After further investigating I realized that it was for our current flight with a divert to ZZZ. I called the flight deck and was told by the flying FO that the IDG message popped up a long time ago and we were diverting to ZZZ and would be landing in less than 60 minutes. By the time we got up into the flight deck we were already well into the arrival. We were not given the actual reason for the divert other than the message came on for the IDG. Ultimately if I had not called the flight deck I'm not sure at what point we would have been contacted about the actual divert. Upon shutting down at the gate the Captain requested some of the printed paperwork not be thrown away as it contained the location of the fuel dump; which was also news to us. No debrief occurred to discuss any of what actually happened while on our break or the incident. In reference to the MX issue I don't think there was much else we could have done as the MX sign off and description of the process seemed adequate at that time. In reference to the lack of communication between the CA and the Relief Pilot's on break I believe this to a breakdown in CRM. When we arrived on the flight deck it was communicated at how much of a cluster it had been and how busy they had been while we were sleeping. I'm still not sure as to the reasoning behind why we were left in the dark on an issue. In my personal opinion leaving out two crew members who could provide assistance; discussion; or generally just keep in the loop of a situation that the CA felt strongly enough to divert; doesn't make sense. Although the CA has the ultimate authority on the decision; working crew members (if time allows for it) should be contacted; if not to be used as a resource; then to keep in the loop. Although we were on break; as working crew members required for the flight we should at least be advised of the necessity of a diversion. Especially since time was not an issue with this particular case.