I think it's incredibly likely that the Colts let Manning go by March 8th (especially now that Polian is gone), where he would be owed $28 Million. If they were to trade him, the cap hit would be something like $18 Million after that? I guess he could restructure the contract to get traded...but why would you want to help them and hurt the team you would be traded to? Makes no sense. And I doubt he'll retire, he even wanted to try and get back and play at the end of this season. Seeing Brett Favre make it oh so close to the SB at age 40, I wouldn't want to retire at 35.
There is a very good chance he becomes a free agent, and I would take the chance on him being healthy. Because if he does get healthy, how could you not want him? We're not getting Luck or RG3, and nobody is going to convince me to trust that Jeff Ireland finds the next Aaron Rodgers. Manning would at least give us a hope of a possible super bowl in the next 3 or 4 years. Take the gamble that he would be healthy...because it's not like we have some superstar waiting in the wings, and don't bring up Matt Moore unless you like kicking Field Goals in the red zone against top teams.
You know Ross would go after him without a doubt if he becomes a free agent. It would fill up every seat and vault the Dolphins into the headlines everywhere, which is something he enjoys. And just imagine how great it would be when the Dolphins go into Indy to play the Colts & Andrew Luck.