Khawaja's problem was that he changed the way he played in test matches. In FC he was more aggressive with his stroke play, while still being patient. In the test matches he played, it looked like he was worried about staying out there a long, long time and to not get out, that he wasn't really looking for runs, which is just asking for trouble. He didn't have a good time in the shield in the games he played since being dropped, so he will have work to do in the UK and at the start of the Shield next season.
His other problem is that now there is now a few young players coming through: Forrest, Cooper, Burns and a couple of older blokes in Quiney and Davis. He will get back in at some stage, he just has to have a strong stint in the UK (if he is playing) and dominate in the shield next year or the next couple of years - A la Hayden.