To remove pluggable database permanently from CDB can use following command:
1. Connect to root and close the pluggable database
[oracle@ora12cn1 Desktop]$ sqlplus / as sysdba
SQL*Plus: Release 12.1.0.1.0 Production on Mon Nov 25 23:21:29 2013
Copyright (c) 1982, 2013, Oracle. All rights reserved.
Connected to:
Oracle Database 12c Enterprise Edition Release 12.1.0.1.0 - 64bit Production
With the Partitioning, Real Application Clusters, Automatic Storage Management, OLAP,
Advanced Analytics and Real Application Testing options
SQL> alter pluggable database pdb2 close immediate;
Pluggable database altered.
2. Issue the DROP PLUGGABLE DATABASE command, you can issue including datafiles or keep datafiles
SQL> drop pluggable database pdb2 including datafiles;
Pluggable database dropped.