Try this.

spool dropusers.sql
SELECT DISTINCT 'DROP USER '||owner||' CASCADE;' FROM DBA_TABLES
WHERE TABLESPACE_NAME = 'EXAMPLE';
@dropusers.sql

alter tablespace example offline;
drop tablespace example;

This will drop all of the schemas that use that tablespace and then drop that tablespace. Which is good as long as you don't have any real data stored there.

Dropping a tablespace with including contents should drop the tablespace and everything in it regardless of RI, Triggers, or indexes.