Easy now, it's a long season. I expect Luck to miss a game or 2 as well but that isn't going to make the season a waste. He could miss the first 4 games, which is still just glorified preseason, and the Colts could be 2-2 with Brissett. I could even see 3-1 with an opening day loss to the Chargers and then wins against TN, ATL, and OAK.
Colts will still be the division champs at 10-6 or maybe even 9-7 with Luck missing 4 games worst case scenario. No reason to hit the panic button on this season yet.