If Cochran doesn't retire, I believe he will face a Tea Party challenge, but I give him a 2/3 chance of surviving it.
If Cochran retires, I imagine the Tea Party candidate will defeat whichever of the Three Stooges from the House runs for the seat.
Thad Cochran is basically an understated version of Robert Byrd - he sends home plenty of "gifts" for his state, but he isn't narcissistic enough to put his name all over them like Byrd did. I think most Mississippi Republicans are aware that were it not for federal dollars being redistributed towards them, their state would be even more of a third world country than it is, even if they don't say it out loud.