I have no idea what happened, but it may be more benign than the ATC Union is making it sound. If one of the IRS went down then they would be back to green world NAV, unable to proceed direct a fix (the Unable RNP MSG). If they were on an RNAV arrival (I have no idea what they were flying), they would have to ask for vectors or be sent to a different arrival. This would cause them to move some other aicraft around if they were given headings. It was the statements from the controller's union that seemed odd (IN CASE they got off course, the pilot had no visuals until below the clouds, there was NO impact to the system, etc). Not once did it say the pilots declared an emergency or asked for priority. IMO, sounds like a good story from the controllers about how an aicraft said they lost some of their instruments (required notification) and asked for vectors while the controllers helped save the day. I'm sure the full story will eventually come out, but the story appears very one sided.