This is not your fault. Not really. And it's galling that the company blamed the incident on the workings of a 'junior engineer'. There was NO DATABASE BACKUP! For Christ's sake. This is live commercial production data. No disaster recovery plan at all. Zilch. And to make matters worse, you were expected to work with a production database when doing development work. This company has not done nearly enough to mitigate serious risks. I don't blame you for quitting. I would. I hope you have found or manage to find a good replacement role.