I am surprised that nobody yet has suggested that you point the aircraft towards the nearest suitable aerodrome! And when I say this you need to point yourself direct to the OVERHEAD (ie not final approach) since at least if you can make the overhead you can spiral down and you will (hopefully) be breaking cloud over a runway where there may be lights and fire cover etc. Also if its a partial failure I would advise the same technique using, if possible, any available power to gain height.
Also if you choose to fly IMC in this situation a slight alteration of the route can reap big safety benefits by avoiding higher terrain and/or routing close to suitable airports for diversion.