If you get an elk down in the backcountry, you're either going to need help getting it out, or you need to be prepared to make several trips to get it out. A downed elk is a lot of work, and keep in mind that leaving ANY edible part of the elk behind is very illegal in most states.
Quartering them isn't too hard, but you can also bone the meat out to lighten the load. Either way, if your hunting in very cold weather, you need to do this BEFORE you make the first trip back to the truck or camp. You never know when something (weather, maybe?) might delay your ability to get back 'till the next day.
It'd be heck to return and find your elk frozen to the point you couldn't cut it up very easily. Yes, I've hunted elk in the backcountry when it was cold enough to do just that.
Stop and think about what you're doing before you do it, and try to think of any problems you might encounter. Having friends to help is great, but if you're stuck doing it alone, you might want to be careful just where you shoot an elk to be sure you can get it out. A smart ol' elk hunter told me once to never hunt downhill from the truck; hunt uphill, and that way it's downhill getting the critter out.
It's good advice, but not always easy to follow. I do know of one fella who got an elk down in really rough country once. They lost one mule that was never found, and never did get the elk out.