How dangerous are Polar Routes, if an aircraft must land on water or wild land?
Depending on where you are it will take around 4 hours to 3 days, if the location is know. Depending on how remote your location is, and if the SAR team knows your location (Sometimes forgotten by pilots after a emergency landing.). If the location isn't known, the search can take up to 2 weeks, finding you and your passengers dead.
Let's say temperature is -10 degrees Celsius, it will take around 1-3 hours without any clothing or external heat source (like a camp-fire) to start hypothermia. Although the critical point of Hypothermia is 25 degrees Celsius, people survived 14 degrees Celsius. The best thing you can do during this plane crash is stay closely together and if possible start a camp-fire. Drink hot water (just take some ice and put it on the fire) with a lot of sugar (or anything else that gives you energy) and just do anything to keep yourself heated until help arrives. 


If possible, keep the navigation lights, strobe lights on of  the plane until battery runs out of fuel. This increases the chance being found in time.