An immunity agreement is almost always contingent upon the accuracy of the information provided, and often on other terms as well (usefulness of the information provided in exchange.) So if he lied to the FBI regarding the info he provided, in a material way (as in, not just a minor item open to interpretation), then it's likely that the Feds could rescind the immunity agreement. However, from what I understand, it's pretty rare for that to happen.

Now... as for the people that Justin has wronged in one way or another (kids he enticed into performing sex acts while underage, people who joined his site because they were told he was of age, and got in trouble because he wasn't), I am pretty sure that they could file civil cases against him... however, it's a little tricky, since he was underage part of the time and of age part of the time.

My guess is that he will probably be slippery enough to get away without any major problems. He seems like a total manipulator who successfully has gotten everyone, including Eichenwald, to buy into his crap.