Today, I just want to share with you on how to create NetworkManager launcher if you have same problem as me - NetworkManager suddenly gone . A simple solution is just to restart your computer.
I have other solution and I want to share it with all of you.
Just follow this guideline :
Right-click on the desktop and Click Create Launcher....

Fill in the details as instructed in the screenshot.

Name: Anything.
NetworkManager Launcher will appear on the desktop. Double-click on the NetworkManager if your NetworkManager suddenly gone. :D