If Nunn doesn't win this year, she could still be pretty potent in 2016.
I agree on that. She could make the Senate race against Isakson pretty competitive, and she would surely be assisted by having an electorate friendlier to her party than the one expected this midterm. Nunn has proven to be a capable candidate in her own right.
I have a hard time seeing her actually beat Isakson, but it will be close and the republicans will have to throw a bunch of money over there to save him. But if Isakson retires, then all bets are off and it probably starts out at Pure Toss-Up.