With or without radar, the times are run on the flight plan. If you lose navigation capability, you resort to dead reconing. Headings should be flown per the flight plan based on ETAs on the flight plan. The radar coverage in S/E Asia is limited to the larger cities at best. Communications are H/F and spotty at best utilizing relays usually through Perth radio.
However, first and foremost, if there was a discrepency with the GPS or IRU plain and simple, don't move the jet. There are more jobs for NG pilots than pilots to fill the seats.
Don't let these scumbags operators compromise your integrity, safety, and your airmans certificates