Restore or reset Oracle database (No Flashback features)
If takeing a rman backup, remember that is has to be an offline backup. Expdp/impdp is an option only if your data is not too big.
You could do filesystem/VM snapshoting depending on your environment.

If your data is of any value to you, please activate the archivelog mode and take consistent backups of your database. The database does it‘s best to safeguard your data please don‘t sabotage the.effort by not takeing backups.