Not to be flippant, but with the nav-aids you are using a map would be the best backup, time and heading (magnetic compass). I have flown many hours in the Canadian arctic with no ground based nav-aids and only unslaved gyroscopes, magnetic compass and my watch as the main nav-aids, some legs approaching 4hrs and have found that a good flight log with winds aloft will normally give you a very good result.
In the event of a simple VOR failure, maintain heading and keep track of the time. It is amazing how well that works if you are cognizant of your system's fallibilities. ie. gyro drift, earth rate, deviation of mag compass, changes in variation, etc. it should put you close to where you want to be.
BD