Delete Bottom Level of a Composite Hierarchy

I have 3 lists and 2 of them have parent hierarchies. The first list and the top level is organization. The second list is cost centers, which has organization as its parent hierarchy. The third list is employees, which has cost centers as its parent hierarchy. If I want to refresh my employee list, deleting all existing employees and reimporting them from a file, is there an easy way to do this without deleting any of the cost centers? Deleting leaf items doesn't seem to work, as that option also picks up any cost centers that don't have employees beneath them.