Forgot to turn off Hotspot, tethered via USB along with direct Ethernet, end result? What happens if I forget to turn off hotspot tethering on my iOS device and connect it via USB to a computer that is already connected to the Internet via Ethernet? Which internet / network gateway gets priority?

I'm concerned because I may have inadvertently wasted large amounts of my carrier's data usage allotment for the month.  Is there a way to avoid this from happening in case I forget to disable the hotspot again? (this is on a Windows PC)

EDIT: As a follow up, how can I configure Windows to require manual input from the User before initiating tethering via a USB-connected iOS device?
I actually think there's little reason to be concerned, provided in Settings > Network, your Wi-Fi or Ethernet is ahead of iPhone USB in the left-hand list. OS X will go down the list and pick the first network provider that it needs to. So long as your WiFi stays up, you're fine.

I confirmed this by opening Network Utility and examining the transfer stats. You can see in the attached screenshots that all the action (packets) are happening over WiFi, hardly anything over iPhone USB.