The longer you are in business, the more likely the possibility that someone who left your employment is going to reapply to return. It helps to have some sort of policy regarding such circumstances so that your employees and managers are aware of the company’s position on such situations. Some employees may leave and attempt to return quickly in order to secure more time off than is otherwise afforded to them. To this end you may want to restrict re-employment to 6 months or more after leaving. Be careful though to allow for the company to address situations on a case-by-case basis. Ohter areas to cover include that of tenure loss, time off accrual, etc., all of which usually go back to zero in the event of a rehire.