After suffering a rib injury against the Dallas Cowboys, the Patriots will not activate LB Dont'a Hightower for the game against the Colts. I believe this is a case of the Patriots managing their injuries and not trying to push one of their key players for just one game. If it were an important game such as a playoff match-up or a need to clinch a playoff spot, he would be suiting up and fighting through the pain. Instead, the Patriots will play it safe and not risk an injury to their defensive signal caller for a regular season match-up against the Colts.
With how important Hightower is, it's a big blow to the defense and it will take more than one guy to fill in the void for the game. Hightower plays multiple roles on the defense as both a traditional linebacker, blitzer, and edge rusher. The Patriots will be looking at Jonathan Freeny, Jonathan Bostic, and Jerod Mayo to take those snaps. Freeny played the edge role in the Dallas game, which he did a solid job at. Mayo will likely take the snaps at linebacker, although I wouldn't be surprised if Bostic gets some reps on the defense soon.
I expect Jamie Collins to get the green dot on defense and a lot more responsibilities handed to him. I had Collins listed as an X-Factor for the game for his ability to do everything asked at the LB position and it looks like he is going to have to do everything for this one. One area the Patriots might suffer in is run defense, since Hightower is better at getting off blocks than Mayo in the run game. That means the interior defensive line has to be able to stand up the Colts OL and allow the LBs to roam free at the 2nd level.
In terms of long term impact, I don't see Hightower being out for an extended period of time. In Week 3 of the NFL season, RB Tevin Coleman suffered a similar injury and only missed two games. The duration of time that Hightower will be out depends on his pain tolerance, which is likely very high since he played with a torn shoulder labrum from Week 15 to the Super Bowl. Not only was he able to play well, he even managed to essentially bench press a 325-lb OT and throw his injured shoulder into Marshawn Lynch and tackled him at the 1-yard line with the help of Akeem Ayers. It will be interesting to see if they activate him for Week 7 against a Jets team that his services will likely needed more than this game.