If everyone on the remaining faction wins, isn't it in the best interests of a UN member to help Secret members fulfill their goals, barring direct conflict (like China-Japan)? Just let all the Secret members win, and kill Sweden, and everybody but Japan, South Korea, Russia, and Sweden will be happy. Which means the real alliances are really those four versus the other seven
Yeah, that came out wrong What I meant is when a single faction manages to eliminate all other players, there's no one stopping them to leave the game, except if their WinCon is no longer possible to achieve.
In your example: if the Secret Alliance manages to kill everybody but let's say Japan already managed to leave alive before this happens, theoretically no one is alive in the game to stop the Secret Alliance members from leaving by killing or imprisoning them. Except that China cannot leave and remains forever trapped since Japan is not dead and already left so cannot die. So in this case only 2 players from the Secret Alliance actually win.
Winning is an individual accomplishment, but most of the time, you need to take a side and help your teammates in order to win.