Unfortuantely if you leave live chess while you're entered in a tournament you will have effectively withdrawn from the tournament without the option to rejoin.
As for the game you just played- all of your live chess games (at least the ones in the last 30 days for basic members) will be visible by going to the live games section of your games archive. Here's a link:
http://www.chess.com/home/game_archive?sortby=&show=live&member=Nf5andwins
Hope that helps!
I was in the middle of a tournament and i wanted to see the game i had just lost. so i made a move on the board and it became the game move. i hoped to find an archived version with the actual game move. no luck, so i went to the home page to see if my game was available somewhere. when i went back to the PLAY page, i was out of the tournament. I was not gone long enough to have missed the start and been disqualified on that account, as far as I could tell.