I don't see him retreating from the war that he started in the first place...He must know full and well the potential of the ninja from all 5 villages and even if he wasn't counting on Naruto or Bee joining the fight I doubt he had not considered it as a possibility.
I don't think anyone really knows what he is fully capable of or what his limits are, and if you ask me he's winning the fight against Naruto/Bee/Kakashi/Guy. Naruto is exhausted from being so involved in the war. Kakashi and Guy have been fighting from the very beginning, and even Bee is tired.
I wouldn't count Tobi out, he's come this far...and I don't think he's about to run away scared.