I'm just wondering if someone can hack the drone and fly it away?? I know that Mavic RC mode Disables Wi-Fi Access node?

I guess this vulnerability is not that critical with these two reasons:
- the attacker most likely only eavesdrops the signal (the risk is similar to connecting WIFI at Coffeeshop)
- the attacker needs to be physically near to your drone (less than 100m?)

I haven't heard of this, I don't think it can be though.

Most certainly it could be.  The Mavic could be hijacked from upto 7km away, the full range of the primary controller.  The 'simplest' hack would be to clone the primary controller thus fooling the drone into accepting the commands from the controller that is closest to the Mavic.  However, 'simple' means the hacker would need access to the primary controller to clone it.  I'm sure a smart hacker could avoid this by 'inserting' a signature/code into the RF signal that fools the Mavic into thinking it is it's unique signature/code, thus controlling any Mavic remotely.  To do this the hacker would need to exploit a fault in the Mavic Firmware.  AS you KNOW...the Mavic Firmware is ROCK SOLID and without any errors...therefore any exploit is unlikely   

DJI Thor Posted at 2017-10-17 19:30
I haven't heard of this, I don't think it can be though.

Here is the paper about it. https://www.krackattacks.com/

Currently this is 'sort of' done by jamming the drone's signals and forcing it to land (auto land).  Not full control but nonetheless this causes the drone to direcly fly away.  Chinese police use such a drone disruptor gun, as do US forces.  Currently there doesn't seem to be any reason to do this, for nefarious use or any other.  Signal jamming a drone is far far easier to do and is the current focus on most anti-drone tech.