Welcome Jason,
Yes, the part he removed is the roller bolt. It appears that he took it out so that the door could be closed, and that the boltwork could be engaged to hold the door shut. You would simply slide that brass bolt back onto the cast post in the lock body to have a working lock again.
You would then be able to test out the combination that was given to you. Everything else appears to be there and in good shape.
If you need further information feel free to post your questions or add photos as your project progresses.