If you are a young adult, but not a student, sports and the university's junior academics are the best sources of social life. Playing league tennis and canoeing on the river are good examples, and there is a world-class kayak race in the middle of town.
The university offers a modestly wide range of films, and classical or folk concerts with international performers. The Morris Centre in town has travelling Broadway shows and occasional performances by the likes of BB King or Bela Fleck. Some such can also be found at colleges and venues in neighbouring towns. There are four major to mid-level degree-awarding colleges in South Bend, and others in the area, so there is a modest market for performers.
The main musical culture of local people is the blues, and proximity to Chicago means that excellent and up-and-coming performers are easy to see. One of the best venues is the Midway Tavern, an old speakeasy on the South Bend side of Mishawaka. Upcoming performances in the area are announced on the Saturday and Sunday blues shows on the NPR station, WVPE, and on the station's website, which has pages of information about events and activities.
It's best to come to South Bend with a willingness to find what's available, rather than wanting to find San Francisco.