Few Questions on scoreboards

I saw the tutorial on scoreboards but there was is a bit more information I need to know.

What happens to the scoreboard after the player quits(leaves the server)? does all the data disappear (score board name etc)

if it doesn't get erased how can I re display it

when I do scoreboard(newScoreboard) does that erase every scoreboard so if i had one for money another for kills it take away both)

if so how do I erase just specific scoreboard out of a bunch of em since that isn't very specific.