I don't know Mo, I think I'm going to have to disagree, though I'll acknowledge ahead of time that there is no good answer here.
If the reports are true that Luck truly IS that once in a generation NFL ready QB, then why not. Right now the Colts are on the decline. Most of their best players are on the downside, and recently they've been horrible in the draft. Time to rebuild their infrastructure..
Why not trade Manning to a team needing "just one more player" for 3 high picks. When you do the numbers what are you losing. Sure he's the 2nd best....now 3rd best QB on the planet, but even if healthy (and that's not an easy guess with a nerve injury), how many more productive years does he have 2....3. So if you are Polian, you are trading at MOST 3 good years of Manning for 15 with Luck....PLUS all the draft picks to surround him with the players he is going to need.....PLUS now you have much more cap room to add quality FAs
I'd do it in a second. The problem is WHO would be willing to give up at LEAST 2 #1s plus other picks AND take on a $20MM cap hit.....even for Peyton Manning? THAT's the reason a deal won't get done....if the Colts wind up with the worst record.