I would suggest you were having a VERY bad day if you had a total nav failure on todays multi redundant a/c. All IRS and GPS fail is unlikely in the extreme.
What made me start this topic was a few weeks ago I was operating back from San Fran in a rare non GPS 747-400, at about 75N over Northern Canada me and the other FO at the controls got an 'unable RMP' message (Rnav Accuracy Monitoring), it started drifting rapidly to about 8 miles ... checked the IRS, of which one seemed 'rouge' but eventually settled down when we briefly picked up a VOR near Baffin (Iqaluit) .... So we were nearly down to 'just' two IRS's ... still no big deal .. but getting uncomfortable ... it would be sods law we would then loose a electrical bus .... I always assume 'if it can happen - it will!'
My company has specific guidlines on what equipment is serviceable to operated into the very Northern latitudes ... but once you are 'there' and it fails .... ???
Yeah ... old style Navigators ... Bring em back!