Default Backup, unroot, and return to stock through ADB?

Unfortunately broke my LG G2 this weekend and want to take it back to get a out of warranty replacement at at&t but assume I need to revert to stock first.

The screen is broken and can not be used but works. Is there a way to back up all my apps with titanium or even a nandroid, and revert to stock using adb maybe? Does any one have a good guide for someone with little experience?

BTW AT&T wants 200 bucks plus tax for the refurbished replacement. Do I got any better options?