Root has been available for the LG G3 from day one. The only version that has not been rooted so far is the Sprint variant. Now that you have root you are probably ready to start modding your device. Root allows you to customize your device, but you can also pretty easily mess things up resulting in a brick. Good news you now have a safety net. Stock KDZ files are available and can be flashed with LGFlashTools. At the very least you should head to the link below and grab the stock files for safe keeping!
Via XDA