This fire sale was coming and Manning likely knew it, which makes it hard to think he'd find sticking around for the rebuilding process very appealing at this stage in his career.
Much as he no doubt wanted to finish his career with the Colts, they wouldn't really be the Colts, or at least the Colts he knew. Not with Clark and Brackett and Addai gone, and the front office seriously shopping Dwight Freeney.
Those Colts are over. What comes next .... well, 'twill be interesting, to say the least.