Part of me (more than part of me in fact) thinks he'll retire, should England win down under. Especuially if he plays well - say a couple of centuries and dragging his average up to (almost) 50.
It wouldn't surprise me if he'd consider 104 tests, 25 centuries, and say 8300 runs at 49 to be enough of a personal legacy for his career.
I think he recognises that although he hasn't lost it, per se, his great innings have become more of nice surprise than the fulfilling of expectation. Although I was delighted with his quickfire 60 in the last match; I just can't help but feel his awareness that he has passed the apex; and his ego will tell him to hang his pads up sooner than later.