B737 First Officer reported during cruise the autopilot disconnected; and they lost all navigational information on the First Officer's side primary flight display.

Narrative

We were assigned to fly from ZZZ-ZZZZ as our second and last leg of the day. We ended up swapping tails after the first jet we were assigned had a maintenance issue. We stepped to the new tail where preflight; taxi; takeoff (Runway XXL); and climbout were expeditious and unremarkable. I was the First Officer acting as Pilot Monitoring and the Captain was the Pilot Flying. We climbed out on the ZZZZZ5 [departure] up to our planned cruising altitude. The entire flight took place in Day VMC. At approximately XA15Z; we were approaching ZZZZZ. The Auto Pilot A" (CA side) had been on for a while at this point with no issues. ZZZZZ is a waypoint on the boundary between the ZZZ1 and ZZZZ1 FIR's approximately halfway across the ocean. Just prior to ZZZZZ; I heard a 'click' and the Autopilot disconnected and my (FO side) PFD lost Airspeed; Altitude; Attitude; Heading; Flight Director (including RNAV course guidance); and several other indications; all replaced with warning flags. The CA's PFD; MFD; Flight Director; FMC; and the Auto Throttle were unaffected and functioned normally; he immediately began to manually control the aircraft. As we began to look around for annunciator lights we noted the IRS2 FAULT light was on; as were the ALTN lights on both EEC's (all on the overhead panel). The CA attempted to reset the Autopilot with no success. As we were rapidly approaching the FIR boundary and the end of US ATC control; I suggested that we request to hold at ZZZZZ; the CA concurred; and I requested the hold with ZZZ1 ATC; who approved the request and let us choose the leg length. We did not declare an emergency at this point. I built the hold in my FMC (both were still working) and the CA's side system displayed and provided Flight Director guidance for him to follow. We began a direct entry turn to the right (to the North) as he and I decided to run the '(NG) IRS FAULT' Checklist. We were fairly certain at this point that the Right Side ADIRU had likely failed. We had great coordination and were very deliberate with each step of the checklist; which led us to decide to select Attitude Mode on the right side IRS (step 10) as I had no useful information whatsoever displayed on my PFD (in accordance with step 9). The checklist directed us to 'Maintain straight and level; constant airspeed flight' for approximately 30 seconds. I let ATC know we would be doing that (we were heading approximately North at this point) and they offered to just let us continue a North Heading in lieu of holding; which we accepted. 30 seconds later; my attitude indicator and heading card were restored (sort of-the heading was operating in free mode and was basically just a directional gyro and had to be routinely updated); but I still didn't have a flight director; navigational guidance; airspeed; altitude; and a couple of other items. Since we were in a degraded navigational state; had great weather between us and ZZZ1; and were still under control of ZZZ1 ATC; the CA decided to return to ZZZ1 (which I agreed with). At some point around this time I sent the first message to Dispatch letting them know we had an IRS2 Failure and would be returning back to ZZZ1. We discussed running the Airspeed Unreliable checklist; which I began to skim; but we decided that it was inapplicable and did not address the issue as the CA side PFD was fully functional and his airspeed indications matched those of the standby instrument. I searched for some way to get airspeed and altitude data from his ADIRU to my PFD; but couldn't find a checklist that could get me there; and there was an ominous warning in the 'Instrument Switching' checklist against linking all navigation information displays to a single source. I pointed out that I still teach at a flight school on the side and am used to flying cross cockpit if need be. I do not recall the exact timing or order of the following; but at some point after I ran the IRS Fault checklist and we were pointed North the following occurred: I noted to the CA that we were no longer RVSM compliant and we requested a descent out of RVSM airspace; ZZZ1 descended us to FL280. An FA called up asking what was going on as pax had noticed that we'd turned around. The purser reported that a passenger was upset and complained that we were kidnapping her. This apparently did not escalate; the FA's later said they were able to calm her down. There were several communications between the CA and the FA's on intercom including a brief. I offered to give the CA a break from hand flying; he gave me the aircraft which I began to hand fly referencing cross-cockpit instrumentation. The CA reviewed the checklist I'd run and ran the '(NG) EEC Alternate Mode' checklist and elected to keep the Auto Throttle ON at the end; the Auto Throttle worked normally throughout the flight. The CA and I coordinated with dispatch on our return to base; and with the flight attendants and the pax on what was happening and why. The CA requested priority handling with ATC and passed his intention to return to ZZZ1. ZZZ1 ATC cleared us direct to ZZZZZ2 for the ZZZZZ2 Arrival; expecting Runway XY (which is what we wanted). ATC told us that XY was unavailable and to expect XZL; I reprogrammed the FMC (the CA was flying again at this point) for the ILS Runway XZL. I attempted to run landing data twice with no success and performance errors. ACARS was working fine the whole time; but landing data just wouldn't come through. I requested it from dispatch who ran if for us and it printed out fine. The Descent; Approach; and Arrival were uneventful. We taxied clear and all the way to the gate."