Even though the Olympic Games will be over, NBC will continue to benefit. People have formed the habit of tuning into NBC. In addition, NBC has been able to advertise their fall lineup. Because of this, people are more familiar with the lineup of shows than they would have otherwise been, so people will be more likely to watch NBC in the fall.
The television ratings for NBC will depend on the quality of their show selection that is offered in the fall. The Olympic coverage has not had a high number of viewers and critics have been negative on the quality of their sports commentary. The Olympic games will not impact the fall ratings.
NBC was hoping the 2016 Olympics would bring them a surge in ratings, but that has not played out so far. One of the biggest factors is that viewership among those aged 18 to 34 has plummeted by nearly a third. Most of these people are probably just looking forward to the Olympics being over, so that they can get back to the preempted programs they normally enjoy.
Because NBC hosted the olympic games on their station, they should have been able to show commerials for their upcoming fall shows. If they did, many who don't regularly watch NBC may be become interested in their shows and will watch shows this fall to see if they like them.