N300 Ext vs. Netgear Router

My stepson set up the N300 in his bedroom for gaming. If he unplugs the power to extender, the main router which everyone else's devices in the house are hooked to, it stops access to the main router or goes to limited rendering the rest of the house "wifi-less".
I know that this shouldn't happen. I searched the forum along with google without finding anything similar. Is there something I can do to stop this from happening? Has the extender become the main router? Is that even possible?

Oh, our main router is the Netgear R6300.

Thank you in advance for any advice that may be offered.