Unless you have a broken polymer lower or you own a now prohibited 180 I don't know why anyone would want to spend the money on the Nodak lower. You're taking a $1500 rifle and turning it into a $2000 rifle to fix an imaginary problem. There have been so few failures that I wouldn't worry about it until it actually happens. If you are unlucky enough to have it break at the front hinge then buy this.
http://stormwerkz.com/accessories/armalite-ar-180b-pivot-repair-section/
If you don't use your rifle as a prybar or release the takedown latch and let the upper swing down and slam into the lower you shouldn't ever have problems. Polymer is not a negative aspect to a rifle, many modern rifles are built with polymer used extensively throughout, ever heard of HK? How about the Bushmaster ACR? I don't see any stories of those rifles breaking apart because of the plastic and they function fine in the winter without becoming brittle and breaking.
Shoot your rifle and worry about fixing it after it breaks, no sense fixing a problem that only exists on the internet, I've only actually ever heard of one person in Canada with a broken lower who swears it broke while shooting and was not a result of abuse. There were a few rifles made years ago that a bad batch of polymer led to numerous failures but Armalite replaced those lowers under warranty and as far as I know those were all US rifles.