Meaning, if the score is 7500 to 2000, if they quit and it migrates it's still at 7500 to 2000.
With the exception of Uncharted 3, they changed it so that the performance dips a bit...you can tell when a host quits because characters will teleport and really funky stuff happens.
All I can say, is make sure the host you switch to is reliable...when they set the host it SHOULD be the guy with the best connection for all players... if he leaves the game is going to get a lot worse for everyone.
Yeah, when I'm doing well it seems they always quit and I get shafted since I had some decent points and objectives banked. This needs to be fixed other wise a lot of time invested in half played matches will accrue and less interest will come of multiplayer.