Head to head
IND V SRL 2-1
AUS V SRL 1-2
AUS V IND 3-1
Possible outcomes
Australia win: Leaves SL and India tied for points; Sri Lanka knocked out on head to head record
Sri Lanka win, Tie or No Result: India knocked out on points alone.
Sri Lanka are the side which have threatened Australia the most. Losing once more would not make them the favourites in the finals. Deliberately losing would be a most boneheaded tactical suggestion, but there's every reason to expect Sri Lanka to train hard for this match and win.
Keeping India in the finals with a victory would afford Australia more of a mental advantage, which they could press at the Gabba. However, India ought to be more comfortable at Adelaide, so they would not be written out of the story by the first loss.
There is also the distinct possibility of rain in each of the remaining games.