I have no experience of such operations, however I would think declare Mayday, Speak to other aircraft and tell them what's going on. ask if any punters have a handheld GPS, If not get a rough track from Sun/Moon (other aircraft could tell you the relative position of the sun/moon for the correct track). use wx radar ground mapping and keep a steady heading until you can positively identify somewhere.
Only my thoughts, be interested to hear what the experts say.