Well WWIV would no doubt start and Motherland being the noob he is would launch his missles forcing us to do likewise and we would be right back to where we are now, all nations gone, mankind wiped out and radiation everywhere.
But if in the slim chance Motherland chose not to launch his missles the armies of UF, Ukraine, SEAC, India would be fighting against the armies of US, CA, a new GUK, Canada, and Europe. The world would be in chaos as armies settle in for a long stalemate as no side has a clear advantage in numbers and nations draft new soldiers by the day to join the armies. Again this would lead to the end of mankind as the recruitment pool would dwindle and deaths overtakes births and the earths population drops from 10 billion to 5 million in just 20 years.
Disclaimer: This is just my belief of how this would have ended. And personally I would have loved to see the latter happen.