Oh man, that's a nightmare scenario! When your entire production line goes down because of a corrupted PLC program and you have no backup, it's pure panic mode. But take a deep breath - here's a step-by-step approach to get you back online safely and minimize that costly downtime:

1. **Safety First - Lockout/Tagout**: Immediately secure the area. Put the entire production line in a safe state, lock out all energy sources, and ensure no one can accidentally start equipment. This prevents injuries while you're working on recovery.

2. **Diagnose the Corruption**: Check the PLC's diagnostic LEDs and error codes. PLC programs can get corrupted by power failures, electrical noise, lightning strikes, or interrupted downloads. Understanding the cause helps prevent recurrence.

3. **Try Memory Recovery**: Many PLCs have built-in recovery modes. Power down the PLC cleanly (abrupt disconnects can make things worse), then initiate firmware recovery mode per manufacturer specifications. Sometimes a flash memory reset can restore basic functionality.

4. **Check for Hidden Backups**: Look for old program versions on engineering laptops, network drives, or even in email attachments. Sometimes there are undocumented copies floating around.

5. **Manual Documentation Review**: Gather all electrical schematics, I/O lists, and operational procedures. These can help you rebuild the program logic from scratch if needed.

6. **Contact Original Programmers**: Reach out to whoever originally programmed the system. They might have personal copies or better memory of the logic structure.

7. **Rebuild in Phases**: If you must rebuild, start with safety circuits and emergency stops first. Then add basic motor controls before tackling complex sequences. Test each section thoroughly before moving on.

8. **Implement Temporary Manual Controls**: For critical processes, consider setting up manual bypass controls to keep essential operations running while you rebuild the PLC program.

9. **Document Everything**: As you rebuild, create comprehensive documentation. This becomes your new backup and prevents future disasters.

10. **Future Prevention**: Once recovered, implement a disciplined backup strategy - store copies in multiple locations (cloud, local server, USB drives) and schedule regular backups. Consider using version control systems for PLC programs.

The key is staying calm and systematic. Safety always comes first, even if it adds a bit more downtime. Once you're back online, make sure this never happens again by establishing proper backup procedures!