Repaired boards get reinspected. Boards that can't be repaired end up in a scrap pile. Once you know how you would use an x-ray system, you'll need to demonstrate that a purchase is economically justified. You should run some financial models to show how an x-ray system can save your company money. The following examples illustrate some of the considerations you should include in your models.
Capacity is sufficient to handle any necessary retests.
For the moment, assume no false failures and no scrap. You decide that increased throughput requires preventing as many problems as possible during PCB assembly and finding any remaining problems as early as possible during testing steps. Now consider PCBs that are more difficult to test. Now assume you're using the information from the x-ray system to improve your manufacturing process. Also, assume that all of the improvements come from correcting manufacturing defects that in-circuit test would find.