/sigh.

How many times was it referenced in this chapter that he was exhausted? The fact that he can fight the battle of a lifetime, be extremely exhausted and weakened, yet still pop into sage mode is a bit... Choose your own word.

edit: Well, the sage mode was primarily to find him again. And since he's already in Sage mode, why get out of it?
He wasn't in sage mode until the page before last.