The adjudicators say they have 90 days to close a case. But when does that clock start? Who knows. Everything is taking an awfully long time.
As far as what happens if your contract ends before your final clearance is granted, I don't know. I am wondering the same thing since my periodic reinvestigation has not been granted and it has been an awfully long time since the investigation closed. Theoretically another company should be able to hire you and pick you up in JPAS, thereby allowing the process to continue... but many companies don't want to mess with that.
Maybe somebody like @marko.hakamaa can weigh in with another opinion on this question.