GPS does not need any kind of internet or wireless connection, but there are technologies like A-GPS that use the mobile network to shorten the time to first fix, or the initial positioning or increase the precision in situations when there is a low satellite visibility.
Android phones tend to use A-GPS. If there is no connectivity, they use pure GPS. They do not override the data network mode. If you deactivated it, the phone won't use any data connection (which is handy if you are abroad, and do not want to pay expensive data roaming).