Had the Colts been able to win just a few more games (and as a result, not get the first or second pick in the draft), Peyton Manning would still be a Colt. The first overall draft pick is an exceedingly rare commodity (hopefully), so they had to pull the trigger and go with Luck. The last time the Colts received the first overall pick in 1998, they drafted none other than Peyton Manning. But had Luck and RGIII not been available, they’d likely have kept Manning who appears to be recovering just fine in Denver.
I still reject the premise that Manning is “one hit away from retirement” (at least, no more than every other NFL player). His pinched nerve is regenerating and he’s regaining the strength in his arm that kept him off the field last season. Other than that, he didn’t all-of-the-sudden become “fragile.” Until last year, he’d never missed a game.