Everyone is making great points. I'd like to add that GOG has dealt with embedded online features before. Let's go back to Fallout 3. The game had a feature to connect to Games for Windows Live, a service that no longer exists. To deal with this, GOG made it so that clicking the button to access GFWL does nothing. The button still exists in the menu, but it has no function. Dragon Age: Origins also did something similar, where the option to connect an EA account exists, but doesn't add anything to the game. Something similar could be done for ME3, where the online component is disabled entirely. I don't think this is a difficult thing to do.