Oracle: Full database (user) restore requires drop?
I haven't found any impdp commands that would allow you to drop existing schema prior to importing data. But you should know that Data Pump command-line utilities are based around PL/SQL packages DBMS_DATAPUMP and DBMS_METADATA. Thus you may well write your own PL/SQL scripts to automate your data move calling programs in DBMS_DATAPUMP directly. And since this is PL/SQL, you may just invoke DROP USER statement in your scripts prior to calls to programs in DBMS_DATAPUMP and DBMS_METADATA.

I think this approach is more flexible, and to further automate your tasks you can employ Oracle Scheduler.