As of yet I'd never had the pleasure (
nopun intended!) but i am sure one, that is to say a single one, would get enough attention and assistance if required. Perhaps one could even decline a short-cut if unable to navigate. Direct BOMBI 150NM out? Punch in FFM, warp 5, and do THE math.
Plenty o'time to go.
However some huge /high alt/ airspace is accesible only for those who are B-RNAV enabled, thus ready to navigate to any given point with certain precision. If unable - not allowed. In a break-down case: "Unable B-RNAV due equipment" as per ICAO Doc 4444/PANS-ATM. Simple as that.
The picture you show reminds me that when we phased out the venerable Tupolev Tu-154Ms dredges, they had been equipped with fleet's most state-of-the-art NAV systems. This was about 7 years ago and still, our common B737/A310 thingies is would be inferior in terms of single unit performance. And, yes, the CDU displays were mounted on F/Os side of the EngIns stack, invisible to the camera shot provided.