My last landlady had a big established plant in her garden and it was the toughest thing ever. You could go out in the middle of winter, scrape some snow off it, and pick green leaves.

I've never tried to start oregano from seed or seedling, and I know a lot of herbs are fragile when they get started. But I think I can safely say that if you can ever get the oregano to thrive at all, you won't be able to kill it after that. :P