If he leaves and regains health, they will have let a future Hall of Famer and the face of their franchise walk away with a few years left in his arm.
That doesn't happen very often.
Unless the Colts choose to keep Manning and give him what he needs to make another run at a Super Bowl, they have to cut him loose.
In fact, they have $28 million reasons to cut him loose before March 8.
The Colts must have medical reasoning to cut Peyton loose, and many expect it to happen in the coming weeks. If they wanted to trade him they'd have to pay the $28 million first. In order to even consider that, Manning would have to be healthy.
Manning isn't healthy. He isn't receiving the bonus, and he isn't going to be wearing a Colts uniform next season either.
Plain and simple, they'll be parting ways and there will be no trade—Manning will walk for free.
The Colts have no control over where he goes once he's released, though.
Sooner than later, Manning will be a free man.