Default [Q] Possible to return to stock state for warranty repair from CM rooted?

Hello!

I'm wondering if its possible to return to stock/unrooted/locked state after G2 was unlocked/flashed to Cyanogenmod as if nothing was done to the device for warranty purposes? I just bought G2 for one of my parents and can't stand the LG skin and have only experience with this with Samsung devices.

What's the story with LG devices, especially LG G2? Looking to flash asap.