Agreed with the majority, AR is a solid reliable rifle, lubed and properly maintained it will always serve you well. Dry she will do just fine. As others have stated, it MIGHT hiccup or jam if you shoot alot of rounds thru it, the average fighting marine or soilder in a COMBAT ZONE carries about 210 rounds, 7 mags, thats a lot of shooting but not enough shooting to jam up a rifle, and a lot of weight to be lugging around. Thats 1 mag in the rifle and 6 shoved somewhere in your pants pockets (assuming you don't have some kinda pack or web gear holding them since that gear would most likely have your cleaning kit and basics too in there) so all that weight is probably what is weighing and pulling your pants down to make you fall in the mud.
If you are in a situation where there are 200 enemies/animals/zombies or whatever coming at you you are already screwing the pooch! If you are falling in the mud and don't have the practical mindset to save your weapon and to keep it as the highest priority on your survival list within reason of course, you may already be lacking in the discipline and patience to survive for weeks alone anyways. Personally if I was lost in the woods, with only an AR, even if I only had one mag, half empty or not, I guarantee you I would clean that thing and maintain it every nite, rub it down with me tshirt, or dry it out and blow the dirt out or whatever. In your scenario, survival is more about discipline and patience than your gear.
Besides a good ole but stroke or strapping on that bayonet will always work in a pinch!