We currently drop dependents who are no longer full-time students. Do we need to then add them when they decide to go back to school? Some dependents are then having multiple events due to not having the required number of credit hours and administration has become a nightmare. Any thoughts to make this easier?

In a similar vein, would a child that was emancipated for a time (married, financially on his own) return to dependent status upon divorcing while yet young enough and moving back home with dad, upon whom he now depends for more than 1/2 of his financial sustenance?

Yes, assuming they still meet the requirements of your plan, you must add them back.