If it ends while in the 5 min waiting period for reconnect then nothing happens. The game added to your record and all stats take effect. If it does end after you are dismissed/kicked for afk then you get -10 mmr as penalty and a leave.
That is what I thought, so I have one more question.
If we have 5 players, when one of them disconnects, you only need 4 votes for a concede. Hypothetically, can this be used for a forced CC? You vote for a cc, one player refuses, you DC, and the game is over?
no it still takes 5 votes until the 5th player completely disconnects (ie after 5 minutes). then it takes 4. so no you can't force a CC like that.