Whenever the Patriots lost Brady, not only were the lucky enough to have a decent QB, but they also didn't have such a specific system like the Colts do. The Colt's offense was built solely around Peyton Manning, which screwed the entire team over. Not to mention that they didn't exactly have that great of an overall team now anyways, Peyton or no Peyton.
If Manning was playing, I would predict that the Colts would find themselves ending around 8-8, or 9-7, with the Texans winning it regardless. I predicted the Texans to win the division this season, long before Manning even had surgery.