Only one team in NFL history has gone 0-16, the 2008 Lions. 5 weeks in there are 3 teams still winless, The 0-5 Colts as well as the Rams and Dolphins at 0-4. How talent poor must a team be in order to fail to win a single game in a 16 game season in a league of parity such as the NFL?
The 2008 Lions scored 16.8 points per game, 27th in the league, and allowed a league high 32.3 points per game. That differential gives a Pythagoren wins (expected wins based off points scored and allowed) of 2.8, showing that it takes (bad) luck as well as (lack of) skill to achieve such a historic accomplishment. The Colts have scored 17.4 and allowed 27.2 which projects to 4.6 wins over a full season.
Of the 2008 Lions' starting 22, just 5 remain with the team this year, all on the offense. Only one player on the 08 Lions (Calvin Johnson) would make a Pro Bowl in the 2008 to 2010 span, while the only former Pro Bowlers to start for the Lions were Daunte Culpepper (5 games) and Kicker Jason Hansen. 6 of their starting 22 are no longer in the league, 7 would never start in the league again and 4 of their starting 22 would never play another game in the NFL.
The Colts have quite a bit more top level talent that those lowly Lions with Freeney and Wayne having as many or more, past Pro Bowl seasons individually than the entire '08 Lions roster, as well as Addai, Mathis, Bethea and Clark with Pro Bowl seasons under their belts. However the Colts do currently have two members of the 2008 Lions on the roster. Linebacker Ernie Simms and Quarterback Dan Orlovsky, both of whom were the primary starters for the Lions that year. Though importantly Orlovsky was only recently added to the roster due to injury and Simms is playing rotationally rather than being a 16 game starter.
As shown by the Pythag wins, it's unlikely that even a team as untalented as the '08 Lions goes 0-16 and the Colts clearly possess significantly more talent on their roster than the 2008 Lions (the Rams and Dolphins almost certainly do as well). The NFL has so much parity and varience that even a truely terrible team is very likely to win several games.
The Colts going winless is about as probable as them fighting to 7 to 9 wins and taking what looks to be a very weak division, in other words, not very likely.