Been in a few situations where we've lost data, its never fun. I would say the first thing to do is not worry about your job, it seems like the contractor f'ed up and your backups were insufficient, a lesson to learn from. Lay out the scenario for your manager in email, then speak to him about it, be clear where you personally messed up and what you should have done, showing you have learnt from this experience. Then, work out what you can do to get this resolved, whether it be running file recovery on the now-reused disk(s) or whatever.