The last time we saw a team have such a dramatic turnaround from their previous season was when the 2008 Miami Dolphins rebounded from a 1-15 2007 season with a 11-5 division winning season. That Dolphins team hosted the same Baltimore Ravens team that eliminated the Colts, and were even held to the same nine points as Indy was held to in a 20-9 loss. The Dolphins have not been heard from since with records of 7-9, 7-9, 6-10, 7-9 and zero playoff appearances. That will not be the fate of the Colts.
This team got massive production in 2012 from Andrew Luck, T.Y. Hilton, Dwayne Allen, Coby Fleener, and even LaVon Brazill had his moments in their passing game. Vick Ballard (best last name in the NFL) led the team in rushing, and seemingly got better and better. ALL of those guys are rookies. We see a sensationally bright future for the Colts.
This organization also has a ton of salary cap space next season. They are likely to lose long-time stud Dwight Freeney, but they will have the resources to replace him (likely someone more excited to play in the 3-4 base defense that Chuck Pagano runs).
Donnie Avery was brought in on a one-year deal, and he was third on the team with 781 receiving yards. Austin Collie missed this season (played in one game) and the word is he may be done in Indy as well. Again, with the roster and money available we see the Colts can replace these guys if they chose to go that route.
Deji Karim and Mewelde Moore are also free-agents, but Indy could chose to go with Donald Brown and/or Delone Carter instead of trying to re-up with either of these guys.