By accident deleted /dev folder on android (LG G2 phone). how can i bring back system to life?
A hard system reset would reset all existing files of the device.

Backing up your files before you committed to the hard reset would be the best course of action for you.

There are step-by-step instructions to assist you in performing the hard reset on the verizon page, but this will work for all carriers as it is the same device: https://www.verizonwireless.com/support/knowledge-base-104173/.