leavers and stats

[Karver]

In starcraft 2 people get an economical bonus when a player leaves could legion and dota do the same? auto loss for the leaver also

This.
I don't know the math behind ELO Gain/Loss but I'm sure you could figure ELO Losses for players with "Leavers" Resulting in less of a loss to the losers/less of a gain to the winners.
Persay: a normal 5v5 Win Sent Loss Scourge all having 1k Elo, Winners get 20 Elo ( These are just guesses ) Losers Lose 20 ELO

Lets say someone leaves on Sentinel now its 4v5. Sentinel loses, Scourge wins, Each loser only loses 16 ELO, Winners only Gain 16 ELO.
(I based ELO on 4 pts per person)
ALSO Due to economical boost, if the 4 Man team WINS, it should include a higher gain then a normal win. (Because of the odds) So In that case, the 4 players get 24 ELO, the losers lose 24 Elo. (or whatever)

OBVIOUSLY Numbers are wayyy off. But I hope you get the idea?

[supersexyy]

If you're with noobs they are more likely to leave - this is already factored into the elo gains/losses.
If you're playing with even teams (which most people should be) then the chance of having a leaver is the same on both teams.