Basically...outside of just worrying about IU handling their own business... looking at all the 1 and 2 loss SEC teams will probably end up determining whether IU makes it or not. And thats really only IF teams like ND and PSU win out, and if BYU goes undefeated in regular season, then loses B12 title game...THEN we might need to worry about the top SEC teams.
Here are the current 1 and 2 loss SEC teams to keep an eye on.
Tennessee (1 loss)
Texas (1 loss)
Texas A&M (2 loss)
Georgia (2 loss)
Ole Miss (2 loss)
Alabama (2 loss)
Missouri (2 loss, but likely too far out for consideration)
If my math is correct, it would take 4 of the teams above beating IU out for an at large, to bump IU completely out of the CFP. And again, that's only if B12 gets two, and ND and PSU win out.
It might not even be possible with how the SEC still has matchups within these teams, to weed themselves out.
In short, this is why IU's chances are so high right now to make the CFP.